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STATS > Probability > Flashcards

Probability Flashcards

1
Q

P(a|b)
(find % given table)

A

do that combined number / b column total

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2
Q

P(A|B^c)
(find percent given table)

A

do all but B in the A column / all but B in the total column

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3
Q

given 2 % numbers find it contains A or B

A

make ven diagram
P(AUB)
make probability /100
add the numerators

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4
Q

given 2 % numbers, find the probability that it contains A or does not contain B

A

make ven diagram
P(AUB^c)
numerator of fraction includes the number on the bottom of diagram and middle /100

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5
Q

given 2 percentages
ex- 40% dogs 32% cats 18% both
find the probability that they own A given B

A

P(A|B)
use formula: P(AandB)/P(A)

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6
Q

independent=

A

same %

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7
Q

given table
is A and B independent?

A

do P(A|B) = %
and P(A) = %

P(A)= total A / total

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8
Q

candy box has 20 chocolates. 14 soft, 6 are hard. Find the probability you pick 3 soft candies in a row

A

14/2013/1912/18

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9
Q

given 3 percent values
ex- a cancer test has sensitivity of 92%, specificity of 89%. assume 4% have cancer

what is the probability you have cancer?

A

do tree diagram
use formula

ex- P(actually have cancer|positive test)
P(A|B)/P(A)
(the first 2) / (1st)(pos)+(2nd)(pos)

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10
Q

soft candy question the 14/20 * 13/19… but they give you a probability

A

(probability)^(how many)

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11
Q

soft candy question the 14/20 * 13/19… but they give you a probability
what’s the probability that 1 is wrong

A

do (probability)^(how many)
then 1- that

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12
Q

given:
P(A)=
P(B)=
P(AnB)=
are A and B independent?

A

so P(A) times P(B)
if it equals the same as P(AnB) then yes independent

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13
Q

complete the two way table
when A and B are mutually exclusive

A

they dont occur at the same time so the top left corner is 0

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14
Q

complete the two way table
when A and B are independent

A

do A/total times B/total
then do that probability times the total

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15
Q

soft candy question the 14/20 * 13/19… but they give you a probability and dont give you how many
what’s the probability that the candy, test, whatever is not right

A

(1-A) times (1-B)

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16
Q

“the detectives found that 40% of the people with food poisoning went to a cocktail party on the second night of the conference”

do P(whatever)
F=got food poisoning
A= attended party

A

P(A|F)
probability that they attended the party was 40% given they got food poisoning

17
Q

given:
P(A)=
P(B)=
what is P(AuB)

A

do A+B - P(AnB)

P(AnB)=multiply A and B

18
Q

what can you compare to P(A|B) to see if its independent

A

P(A) and P(A|B^c)

19
Q

discrete random variable

A

YES gaps (NO decimals)
1, 2, 3, 4

20
Q

continuous random variable

A

NO gaps (YES decimals)
1, 1.1, 1.2

21
Q

P(X>=3)

A

add numerators / total

22
Q

how to calculate mean

A

E(x)= X(P%)+X(P%)+x(P%)

23
Q

how to calculate mean/SD in calculator

A

stat, edit, 12345 and probability, stat calc edit, L1, L2, calculate

24
Q

how to describe mean

A

“If I choose many many ___(ppl, gum)___ , the average number of __(ppl, gum)__ in __fam, pack___ will be ___

25
Q

How to describe SD

A

The number of __(ppl, gum)__ typically varies __#___ (ppl,gum) from the mean __#__ (ppl, gum)

26
Q

X: 1, 5, 7 , 10
P: 3/23, 4/23, 4/23, 9/23
it this discrete or continuous

A

discrete

27
Q

percentages on graph

A

.1, 2.1, 13.6, 34.1

28
Q

graph: what is the probability that they do more than 20

A

do 20- mean
that answer is z score
find that on chart
if right side shaded, 1- that
move decimal into %

29
Q

if youre adding a constant in your formula T=Y+4
then how would the mean and SD change

A

mean would add by 4
SD would stay
shape would stay

30
Q

can u calculate the total mean of 2 variables that already have means by just adding their means together

A

yes, can be independent or dependent and will work

31
Q

can you calculate the total SD of 2 variables that already have SD by adding them ^2 together and square root

A

if independent- yes
if not independent- no

32
Q

How do you find SD of 2 variables that are already given SD and are independent

A

square them, add them, then square root

33
Q

what does independent random variable mean

A

X has no relation to the outcome of Y

34
Q

X= test score from grade 9
Y= test score from grade 10

are these independent random variables

A

yes because one grade does not help us predict the grades of another grade

35
Q

what do you put in calc to calculate a binomial with x>4 versus x<4

A

x>4 then 1-binomcdf
x<4 then binomcdf

36
Q

what do you put in calc to calculate a binomial with x>=4

A

then 1-binomcdf(n,p, 3)

37
Q

“at most 3”

A

x<=3

STATS (4 decks)

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