Speed Mathematics

Question 1

What is the easiest way to substract 9?

Answer 1

Take away 10, then add 1 to the answer.

Question 2

What is the easiest way to substract 8?

Answer 2

Take away 10, then add 2 to the answer.

Question 3

What is the easiest way to substract 90?

Answer 3

Take away 100, then add 10 to the answer.

Question 4

What is the easiest way to substract 80?

Answer 4

Take away 100, then add 20 to the answer.

Question 5

What is the easiest way to substract 70?

Answer 5

Take away 100, then add 30 to the answer.

Question 6

What is the easiest way to substract 7?

Answer 6

Take away 10, then add 3 to the answer.

Question 7

78 / 2

Answer 7

80 - 2. Half of (80 - 2) is (40 - 1). That is your answer.

40 - 1 = 39

Question 8

38 x 2

Answer 8

Think of (40 - 2). Double would be (80 - 4) = 76.

Question 9

To add 9 …

Answer 9

…add 10 and substract 1.

Question 10

To add 8 …

Answer 10

…add 10 and substract 2.

Question 11

To add 7 …

Answer 11

…add 10 and substract 3.

Question 12

To add 47 …

Answer 12

…add 50 and substract 3.

Question 13

To add 196 …

Answer 13

…add 200 and substract 4.

Question 14

To add 38 …

Answer 14

…add 40 and substract 2.

Question 15

To add 288 …

Answer 15

…add 300 and substract 12.

Question 16

Addition: If the units digit is high, …

Answer 16

…round of to the next ten and then substract the difference.

Question 17

Addition: If the units digit is low, …

Answer 17

…add the tens, then the units.

Question 18

$4.95 + $6.95 + $13.95

Answer 18

$5 + $7 + $14
- 15¢

= $25.85

Question 19

495 + 695 + 1395

Answer 19

500 + 700 + 1400
-15

= 2585

Question 20

8461 + 5678

Answer 20

8 + 3 = 13 (13,000)
4 + 6 = 10 (14,000)
+ 61 (14,061)
+ 78 (add 100 and substract 20, then substract 2)

= 14,139

Question 21

6 + 8 + 4

Answer 21

6 + 4 = 10
+ 8
= 18

Question 22

When adding a column of numbers, …

Answer 22

…add pairs of digits to make tens first, than add the other digits.

Question 23

463 - 87

Answer 23

436 - 100 = 336
+ 13 (add 10 + 3)
= 349

Question 24

134 - 76

Answer 24

24 + 34 = 58

Question 25

A good general rule for dividing by factors is to …

Answer 25

…divide by the smaller number first and then by the larger number.

Question 26

3,444 / 21

Answer 26

3,444 / 3 = 1,148
1,148 / 7 = 164

Question 27

To divide by a two-digit number ending in 5, …

Answer 27

…double both numbers and use factors.

Question 28

29 x 8

Answer 28

30 x 8 = 240
240 - 8 = 232

Question 29

The general rule for standard long division

Answer 29

Round off the divisor to the nearest ten, hundred or thousand to make an easy estimate.

This way you’re able to make an easy estimate and then proceed in the usual way to correct as you go.

Question 30

If you’re dividing by 31, …

Answer 30

…round of to 30 and divide by 3 and 10.

Question 31

If you’re dividing by 87, …

Answer 31

…round of to 90 and divide by 9 and 10.

Question 32

If you’re dividing by 321, …

Answer 32

…round of to 300 and divide by 3 and 100.

Question 33

If you’re dividing by 487, …

Answer 33

…round of to 500 and divide by 5 and 100.

Question 34

If you’re dividing by 6,142, …

Answer 34

…round of to 6,000 and divide by 6 and 1000.

Question 35

To convert 80kg to pounds…

Answer 35

…calculate 80 x 2.2

double 80 to get 160,
then multiply this by 11 (1,760),
and divide by 10 to get 176 pounds

Question 36

90kg in pounds

Answer 36

90 x 2 = 180

180 x 11 = 1,980

1,980 / 10 = 198 pounds

Question 37

An easy way to divide any two-digit number by 9 is…

Answer 37

…to take the tens digit as the answer, and add both digits of the number for the remainder.

42 / 9
= 4 r6

34 / 9
= 3 r7

Question 38

71 / 9

Answer 38

7 r8

Question 39

Often, when you have to multiply two number, the calculation can be made easier if you…

Answer 39

…can double one number and halve the other.

Question 40

3 x 14

Answer 40

= 6 x 7
= 42

Question 41

An easy way to divide by 15 is to …

Answer 41

…double the number and divide by 30.

Question 42

An easy way to divide by 25 is to …

Answer 42

…double the number and divide by 50.

Question 43

An easy way to divide by 35 is to …

Answer 43

…double the number and divide by 70.

Question 44

An easy way to divide by 45 is to …

Answer 44

…double the number and divide by 90.

Question 45

2,341 / 35

Answer 45

= 2,341 x 2 = 4,682

= 4,682 / 10 = 468.2

= 468.2 / 7 = 66.8857

Question 46

20000000 - 52316

Answer 46

20000000
-0052316
= 19947684

Question 47

To change Fahrenheit to Celsius, …

Answer 47

…substract 30 degrees and then halve*

*close enough for practical purposes.

Question 48

To change Celsius to Fahrenheit, …

Answer 48

…double and then add 30*.

*close enough for practical purposes.

Question 49

One foot is …cm.

Answer 49

…approximately 30cm.

Question 50

One inch is …cm.

Answer 50

…approximately 2.5cm.

Question 51

1 mile is …km.

Answer 51

…approximately 1.6km.

Question 52

1 km is …miles.

Answer 52

…approximately 0.6 miles.

Question 53

1kg is …pounds.

Answer 53

…approximately 2.2 pounds.

Question 54

1 pound is …kg

Answer 54

…approximately 0,45kg.