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GRE Math > GRE Math Formulas > Flashcards

GRE Math Formulas Flashcards

0
Q

Distance =

A

Rate*time

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1
Q

Average rate?

A

Total distance/ total time

or

Total earnings/ Total time

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2
Q

Work =

A

Rate * time Work= individual rate • number of workers • time

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3
Q

Difference of squares

A

X2 -Y2 = (x+y)(x-y)

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4
Q

(X+Y)2

A

X2 +2xy+y2

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5
Q

45-45-90 triangle

A

1:1: root 2

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6
Q

30-60-90 triangle

A

1:square root of 3: 2

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7
Q

Diagonal of a rectangular box

A

D squared = L squared + W squared + H squared

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8
Q

Height of equilateral triangle

A

H=S * sq. root of 3/ 2

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9
Q

SA of cube

A

6(side)2

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10
Q

Volume of cube

A

(Side)3

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11
Q

Volume of rectangular box

A

L*W*H

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12
Q

Arc length =

A

Sec angle/360 * 2(pi)(R)

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13
Q

Volume of circular cylinder

A

(Pi)(r2)(H)

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14
Q

Path. Triangle shortcut

A

5-12-13 3-4-5 8-15-17 7-24-25 9-12-15

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15
Q

Surface area of box

A

2(L*w)+2(h*L)+2(h*w)

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16
Q

Area of a trapezoid

A

A=(b1+b2)/(2)

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17
Q

Area of a polygon

A

A=B(H)

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18
Q

Sum of angles

A

180(N-2)

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19
Q

Is it possible for 2 events to happen at the same time? Yes.

A

P(a) or p(b) = p(a)+p(b) - p(a and b)

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20
Q

Is it possible for two events to happen at the same time? No.

A

P(a) or p(b) = p(a)+p(b)

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21
Q

When one event happens does this influence/change the outcome of the other? Yes.

A

P(a and b) = p(a) • p(b|a)

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22
Q

When one event happens does this influence/change the outcome of the other No.

A

P(a and b) = p(a) • p(b)

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23
Q

Area of polygon with diagonals

A

A= D1+D2/2

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24
Q

Solve a part:part:whole

A

4:1:50 5x=50 X=10

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25
Q

Chase problems

A

Subtract 2 cars rate together. 80-50=30 miles per hour. Distance of 50 miles north D=RT 50=30t 5/3=t

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26
Q

Collision problems

A

Add 2 cars rate together. 40 + 56 = 96 D=RT d=1200 1200=96t T=12.5

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27
Q

Regular pentagon

A

All sides and all angles are equal

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28
Q

nCr

A

1st r values of n!/R!

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29
Q

Find the Nth number in a sequence

A

1st term + pattern(n-1)

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30
Q

Find the sum of a sequence

A

1st term + 2nd term/ 2= average Average • # of terms = sum

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31
Q

Students at a school 2/5 - take german 1/7 - take French 1/3 - take Spanish 25 - take Portuguese How many students are there?

A

7•5•3 = 105 42/105 + 15/105+ 35/105 = 92/105 26 represents 105/105 - 92/105 = 13/105 26=13/105m M=210

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32
Q

1/4 of juniors and 2/3 of seniors are going. If there 2/3 as many juniors as seniors. What fraction of students are not going?

A

2/3 as many juniors as seniors 20 - juniors 30 - seniors Juniors on trip 1/4(20)=5 Seniors on trip 2/3(30) = 20 50 total student. 25 going. 25 are not going.

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33
Q

√2

A

1.4142

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34
Q

√3

A

1.732

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35
Q

Percent change

A

Difference/original * 100

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36
Q

75 is reduced by x% is 54 X=??

A

75 minus x percent 75 is 54. 75 - 75/100x = 54 75-54 = 3/4x 21(4/3)=x 28=x

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37
Q

Root 2

A

1.4142

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38
Q

Root 3

A

1.732

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39
Q

Percent change

A

Difference/original * 100

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40
Q

Average =?

A

sum of n numbers/n

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41
Q

Range

A

greatest value - least value

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42
Q

Pens cost £0.70 each, and pencisl cost £0.40 each. If Jakob spent £5.20 on 10 pens and pencils, how many pencils did he purchase?

A

Number of pencils = x

number of pens = 10- x

(Cost per pen x number of pens) + (cost per pencil x number of pencils) = total cost

70(10-x) + 40x = 520

700 -70x +40x = 520

700-30x=520

180 = 30x

x=6

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43
Q

Marco is twice as old as Vladimir. Four years ago, Marco was 6 years younger than 3 times Vladimir’s age at that time. How old will Marco be in 2 years?

A

M = 2V

M-4 = 3(V-4) - 6

M-4 = 3V-12-6

2V-4 = 3V-18

2V+14=3V

14=V

2(14) = 28 +2 = 30

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44
Q

Movie Theater charges £6 per ticket and each movie showing cost the theatre £1,750. How many people need to see a movie so that the theater makes £1 of profit per customer?

A

c=6c-1750

-5c=-1750

c=350

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45
Q

Mr Choudury’s class consists of 20 students: 12 boys and 8 girls. If the boys weigh an average of 80 pounds each, and the girls weigh an average of 70 pounds each, what is the average weight in pounds of all 20 students

A

12 boys x 80 pounds per boy = 960 pounds

8 girls x 70 pounds per girl = 560 pounds

total = 1,520 pounds

1520/20 = 76 pounds

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46
Q

What percent of y percent of 50 is 40 percent of y?

A

(X/100)(Y/100)50 = (40/100)y

(X/100)(Y/2)= (2/5)y

x= 2y(100)(2)/5y

x=80

47
Q

A chemist is mixing a solution of acetone and water. She currently has 30 ounces mixed, 10 of which are aretone. How many ounces of acetone should she add to her current mixture to attain a 50/50 mixture of acetone and water if no additional water is added?

A

50/100 = 10+x/30+x

1/2= 10+x/30+x

Cross multiply: 30+x=20+2x

10=x

48
Q

Jane scored 15% higher on her secont test than she did on her first test. Jane’s score on her third testwas a 25% decrease from the score on her second test. If Jane got a 69 on her third test, what was her score on her first test?

A

x(1.15)(.75) = 69

x=80

49
Q

A hunting lodge has enough fuel to keep 20 rooms heated for 14 days. If the lodge decides to save fuel by turning off the heat in 5 unoccupied rooms, and each room requires the same amount of fuel to heat it, how many FULL days will the fuel supply last?

A

20(14) = 280

280/15 = 18.67

18 FULL days

50
Q

Car A driving north frompoix X, traveling at a constant rate of 40 miles per hour. One hour later car B started driving north from point X at a constatn rate of 30 miles per hour. Neither car changed direction of travel. If each car stated with 8 gallons of fuel, which is consumed at a rate of 30 miles per gallon, how many miles apart were the two cars when car A ran out of fuel?

A

Car A’s distance - Car B’s distance = distance between cars

Car A: 30 miles per gallon x 8 gallons = 240 miles

240/40= 6 hours

Car B: (30 miles per gallon)(6 hours - 1 hour) = 150 miles

240-180= 90 miles apart

51
Q

One robot, working independently at a constatn rate, can assemble a doghouse in 12 minutes. what is the maximum number of complete doghouse that can be assembled by 10 such robots each working on separate doghouses at the same rate for 2.5 hours?

A

Individual hourly rate is 60/12 = 5 doghouse/ hour

each robot produces 5 x 2.5 = 12.5 doghouses in 2.5 hours

total of 12 x 10 = 120

52
Q

A rectagle’s width w is twice is length. Express the rectangle’s area in terms of w?

A

w=2L

in terms of w solve for L

L = w/2

A=L x W

A = w x w/2

= W^2 / 2

53
Q

2:3 ratio of boys to girls. 4:3 ratio of students from northside to southside.

number of students?

A

2x+3x = 5x

3y + 4y = 7y

5 x 7 = 35

54
Q

Arjen’s tennis record was 3 matches won for every 2 matches lost. If he played 30 games last season how many did he win?

A

part: part: whole
3: 2:30

3x+2x = 30

5x=30

x=6

6(3) = 18

55
Q

At an animal shelter, the ratio of cats to dogs is 4 to 7. If there are 27 more dogs than cats. how many cats are at the shelter?

A

“there are 27 more dogs than cats” becomes Dogs- cats or

7x-4x = 27

3x=27

x=9

4(9) = 36 cats

56
Q

On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain number of girls joined and twice that number of boys left, changing the ratio of girls to boys to 7:4. How many boys left?

A

Girls / Boys = 8+x/20-2x = 7/4

4(8+x) = 7(20-2x)

32 + 4x = 140 -14x

x=6

2(6) = 12 boys

57
Q

Cranberry juice is 3 parts cranberry and 1 part seltzer. Lemonade is 1 part lemon juice and 2 parts seltzer. one glass of cranberry is mixed with an equally sized glass of Lemonade.

A

Cranberry:Seltzer: whole = 3:1:4

Lemon: Seltzer:whole = 1:2:3

Since the two glasses are the same size, choose a smart number.

Multiply Cranberry ratio by 3 and Lemonade by 4.

Cranberry:seltzer:whole = 9:3:12

Lemon:seltzer:whole = 4:8:12

Total of 24 ounces 11 seltzer water

58
Q

Oil, vinegar, and water are mixed 3:2:1 to make dressing. If Jozef has 8 cups of oil, 7 cups of vinegar, what is the maximum number of salad dressing he can make?

A

3:2:1 = 6 cups of dressing

8/3 x 6 = 18 cups of dressing

59
Q

5/8 of weekly salary on rent. 1/3 of remaining on food. £40 available for other expenses.

weekly salary?

A

5/8 of salary is spent on rent. 1-5/8 = 3/8 of salary remaining. Of remaining spent 1/3 on food.

(2/3)(3/8) = 2/8 = 1/4

1/4x = 40

x = 160

60
Q

Mixture of acid and water in a ratio of 1:2. After 200 mL of water is added, the ratio of water to acetone is 2:3. The original volume of the mixture?

A

water/ acetone = x+200/2x = 2/3

3x +600 = 4x

x=600

original volume of water is 600 mL while the orginal volume of acid is 2x = 2(600) = 1200. Total is 600+1200= 1800

61
Q

Ratio of Noah’s time to Matthieu’s to paint a house is 3:5. If Noah and Matthieu work together at their respective rates, they can paint a house in 10 hours. How long does it take Noah to paint a house alone?

A

1/3x+1/5x = 1/10

5/15x+3/15x = 1/10

8/15x = 1/10

15x = 80

x = 16/3

3(16/3) = 16 hours

62
Q

In a certain town, 2/5 of the population is employed. Among the unemployed population, the ratio of men:women 5:7. if there are 40,000 employed people in the town, how many females are unemployed?

A

Employed/Total pop. = 40,000/x=2/5

2x=200,000

x=100,000

Unemployed population = 100,000-40,000 = 60,000

Unemployed females/Total unemployed = y/60,000 = 7/12

= 35,000 unemployed females.

63
Q

A zoo has twice as many zebras as lions and four times as many monkeys as zebras. Which of the following could be the total number of zebras, lions, and monkeys at the zoo?

  1. 14
  2. 22
  3. 28
  4. 55
  5. 121
A

Lions: Zebras: Monkeys = 1:2:8

(1+2+8) = 11

Must be a multiple of 11

22,55,121

64
Q

Average population in town x was recorded at 22,455 during to years 2000-2010, inclusive . An error was later uncovered: the figure was erroneously recorded at 22,478 in 2009, but should have been 22,500. What’s the average?

A

There are 22 people not counted.

11 years

divide 22/11 = 2

the average should be 2 more

New average is 22,457

65
Q

For any evenly spaced set?

A

the median and mean are equal

66
Q

Standard Deviation

A

A measure of how spread out the numbers in a set are - the more spread out he numbers, the larger the standard deviation.

Standard Deviation is the average distance the data values are away from the mean.

67
Q

What is a quartile?

A

defined as teh median of half of a set of data

68
Q

Data Set: 1, 3, 4, 6,6

What is the standard deviation

A

Mean = 20/5 = 4

Distance from mean

4-1 = 3

4-3 = 1

4-4=0

6-4=2

6-4=2

–> 3+1+0+2+2 = 8/5 = 1.6

69
Q

Standard Deviation of (22,22,22,22)

A

0

70
Q

Variance?

A

(Standard Deviation)2

71
Q

Standard Deviation is 3, what is the variance?

A

Var = 32

= 9

72
Q

Set A (5,7,8,9,11,14,15,15,18,18)

If set A has a mean of 12 and a standard deviation of 4.4. How many numbers in set A are within in 1 unit of Standard Deviation from the mean?

A

12 + 4.4 = 16.4

16.4+4.4 = 20.8

12-4.4 = 7.6

7.6-4.4 = 3.2

Numbers between 7.6 - 16.4

6 numbers!

73
Q

Within 1 Standard deviation of the mean

A

34% on both sides = 68%

74
Q

Within 2 standard deviation of the mean

A

13.5 on both sides plus the exisiting 65% = 95%

75
Q

Within 3 standard deviations of the mean

A

2.5% on both sides = 5%

+ 95% = 99%

76
Q

Set A ( 2,4,7,9,4,5,9,4,9,2,11,2,3,4,3,4)

Find Q1, Q2, Q3

A

First reorder set

(2,2,2,3,3,4,4,4,4,4,5,7,9,9,9,11)

Find Median = 4+4 = 8/2 = 4

Median = Q2 = 4

Q1 = median of lesser numbers

Middle term = N+1 / 2

8+1 = 9/2 = 4.5 between 4th and 5th term.

Q1 = 3+3 = 6/2 = 3

Q3 = median of the greater numbers

16/2 = 8

Q3 = 8

77
Q

For finding quartiles if the amount of numbers in the data set is odd?

A

The median is excluded from both lesser and greater numbers

78
Q

If a score is in the 40th percentile in a large distubution….

A

the score is larger than 40% of the distrubution

79
Q

Percentile of the lowest score is…

A

the 0th percentile

80
Q

Percentile with the highest score…

A

the 99th percentile

81
Q

Percentiles for normal distrubtions

A

M - 2d = 2.5th

M - d = 16th

m = 50th

M + d = 84th

M+2d = 99th

82
Q

what is the probabilty that a month has an R in it?

A

4 months do not have an R - May, June, July, August.

12-4 = 8

8/12 = 2/3 = 66.67%

83
Q

Approximate rules

A

“Or” means add

“and” means multiply

84
Q

Complement of A

ex: Probablity that Denmark does not win the World Cup.

A

P(not A) = 1 - P(A)

85
Q

With Replacement

A

Whatever selection is drawn put it back into deck and make the next choice from a full/ new shuffled deck.

Each new choice is indepedent of previous

86
Q

Without replacement

A

pick a card, place it aside. each new choice is from a smaller deck.

Each new choice is made under a different condition. And the probability for all successive choices is NOT independent.

87
Q

What is the prob of tossing 3 coins, and getting 3 heads?

A

Each flip is independent from each other.

1/2 x 1/2 x 1/2 = 1/8

88
Q

What is the probabilty of rolling 2 six sided dies and getting snake eyes?

A

The rolls are indepedent of each other.

1/6 x 1/6 = 1/36

89
Q

3 cards are selected with replacement. what is the probabilty of selecting 3 spades in a row.

A

With replacement, the selections are independent of each other.

1/4 x 1/4 x 1/4 = 1/64

90
Q

Events A and Events B are independent. (Not Mutally exclusive) If P(A) = 0.6

P(B) = 0.8

What is the probabilty of A or B happening?

A

P(A or B) = P(A) + P(B) - P(A and B)

  1. 6 + .8 - (0.8 x 0.6)
  2. 4 - .48 = .92
91
Q

A box has 5 green balls, 7 red balls. Picked with out replacement, what is the probabilty that the 1st 2 balls are both green.

A

total of 12 balls.

P(1=g) = 5/12

P(2=g/ 1=g) = 4/11

5/12 x 4/11 = 5/33

92
Q

52 cards, probabilty of picking 3 hearts without replacement.

A

P(1) = 1/4

.25 x 52 = 13

P(2=H | 2=H) = 12/51 = 7/17

P(3=H | 2=H, 1=H) = 11/50

1/4 x 7/17 x 11/50 = 11/850

93
Q

Formula for binomials

A

P= (nCr) x (Pr) x [(1-P)n-r]

P= Probabilty of successes

R = Number of successes

N = Number of trials

94
Q

10 dice are rolled, what is the probability of rolling 2, 5s.

A

10c2 = (1/6)2 x (1-1/6)10-2

(1/6)2 x (5/6)8

95
Q

When you see the words “at least” in a probability question…

A

use complementary rule.

P(not A) = 1 - P(A)

96
Q

Roll one die, 8 times. What is the probabilty that we will roll at least one 6.

A

The complement of at least one 6 is zero 6s.

Probabilty of not getting a six in one roll = 5/6

Probablity of not getting a 6, 8 times = (5/6)8

P= 1-(5/6)8

97
Q

Cars can be made with gas, hybrid, or electric power. They can be red, black, blue. and the transmission can be either automatic or standard.

how many different cars are possible?

A

3 types of power x 3 colours x 2 transmission

= 18 types of cars

98
Q

There are 2 girls and 3 boys.

How many different ways can we seat kids in a row if the girls must sit on the end.

A

2 x 3 x 2 x 1 x 1

= 12

99
Q

Lukas, Jakob, Misha, Aleksandr, and Uli are racing. If each person finishes a race and no one ties. How many different possibilities are there?

A

5 x 4 x 3 x 2 x 1 = 120 or 5!

100
Q

How many ways can we rearrange 9 letters in the word WONDERFUL

A

9!

9 x 8 x 7 x6 x 5 x 4 x 3 x 2 x 1 = 362,880 ways

101
Q

How many ways can 5 letters JKLMN be arranged so that L is not in the middle.

A

2 ways to solve this problem.

1) Adhere to restriction: 4 x 3 x 4 x 2 x 1 = 96

or

Ignore the restriction : 5 x 4 x 3 x 2 x 1 = 120

Break the restriction: 4 x 3 x 1 x 2 x 1 = 24

120-24 = 96

102
Q

How many different ways can the word STUDY be rearranged

A

5 x 4 x 3 x 2 x 1 = 5! = 120

103
Q

How many different ways can the word NANNY be rearranged.

A

Total number of letters! / number of letters that repeat !

5! / 3!

5 x 4 x 3 x 2 x 1 / 3 x 2 x 1 = 20

104
Q

How many ways can the word MISSISSIPPI be rearranged.

A

M - 1

i - 4

S - 4

P - 2

11! / 4! 4! 2! = 34,650

105
Q

Comination Formula

A

nCr = n! / r! (n-r)!

106
Q

From your group of 5 friends, select 3 to join on a camping trip. In how many different ways can you select 3 friends.

A

5c3 = 5! / 3! (5-3)!

5! / 3! 2!

20/2 = 10

107
Q

When to use cominations.. does the order matter?

A

No? then use combinations!

Yes? then use Fundamental counting principle

108
Q

12 toppings, how many 3 toppings pizzas can be ordered?

A

Order does not matter.

12C3 = 12! / 3! (12-3)!

= 12! / 3! 9!

= 200

109
Q

There are 8 people in a room, everyone shakes hands. How many handshakes.

A

Does the order matter? No.

8C2 = 8! / 2! (8-2)!

= 8! / 2! 6!

110
Q

From a group of 10 members, 3 are randomly selected, one as chair, one as treasurer, and one as secretary. These 3 will form a “board” of committee. How many possible boards can be formed?

A

Does order matter? Yes!

10 x 8 x 9 = 720 ways

111
Q

In a set of 10 million numbers, one percentile would represent what percent of the total number of terms?

A

A percentile ALWAYS represents one percent of a set of data.

= 1

112
Q

Percentiles from mean and standard deviation

A

M-2d = 2.5th

M-1d = 16th

M = 50th

M+d = 84th

M+2d = 97.5th

113
Q

150 Students, 75 take latin, 110 take spanish, 11 take neither. Number of students that take only latin?

A

Total = Group 1 + Group 2 - Both + Neither

150 = 75+110-B +11

B = 46

75-46 = 29

114
Q

There is an 80% chance David will eat a healthy breakfast and a 25% chance that it will rain. If these events are independent, what is the probablity that David will eat a healthy breakfast OR it will rain.

A

P(A)+P(B) - P(A and B)

.8 x .25 = 0.2

1.05-.2 = .85

GRE Math (3 decks)

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