FastMath Practice

Question 1

How to multiply by 25

Answer 1

Divide by 4 then multiply by 100

Question 2

How to divide numbers with multiples of 4 by 4?

Answer 2

Left to right, digit by digit. Ex: 84/4 –> 8/4 = 2 and 4/4 = 1, concatenate to 21

Question 3

How to divide numbers with non-multiples of 4 by 4?

I.e. 52/4

Answer 3

I.e. 52/4 –> decompose

• -> 40/4 = 10
• -> 12/4 = 3
• -> concatenate to 13

OR divide by 2 twice

52/2 = 26 –> 26/2 = 13

Question 4

8*25

Answer 4

8÷ 4 = 2

2 *100 = 200

Question 5

25*55

Answer 5

44 ÷ 4 =11

11*100 =1,100

Question 6

16*25

Answer 6

16/4 = 4
4*100 = 400

Question 7

25*40

Answer 7

40/4 = 10
10*100 = 1000

Question 8

24*25

Answer 8

24/4 = 6
6*100 = 600

Question 9

25*60

Answer 9

60/4 = 15
15*100 = 1500

Question 10

320 * 25

Answer 10

320/4 = 80
80*100 = 8000

Question 11

25*18

Answer 11

450

Question 12

26*25

Answer 12

26/4 = 6.5 –> 6.5*100=

650

Question 13

25*9

Answer 13

9/4 = 2.25 –> * 100 = 225

Question 14

17*25

Answer 14

425

Question 15

25*900

Answer 15

22,500

Question 16

25*800

Answer 16

20,000

Question 17

160*25

Answer 17

4,000

Question 18

1,200*25

Answer 18

30,000

Question 19

25*140

Answer 19

140/2 = 70
70/2 = 35
35*100 = 3,500

Question 20

860*25

Answer 20

860/2 = 430
430/2 = 215
*100
21,500

Question 21

25*124

Answer 21

3100

Question 22

180*25

Answer 22

4,500

Question 23

25*328

Answer 23

8,200

Question 24

How to divide by 25

Answer 24

25 = 100/4, so

1. Multiply by 4 (or multiply by 2 twice) and then divide by 100
   OR
2. Divide by 100 and then multiply by 4

Question 25

300/25

Answer 25

``` 300/100 = 3 3*4 = 12 ``` OR 300*4 = 1200 1200/100 = 12

Question 26

700/25

Answer 26

``` 700/100 = 7 7*4 = 28 ```

Question 27

1,200/25

Answer 27

``` 1,200/100 = 12 12*4 = 48 ```

Question 28

900/25

Answer 28

``` 900/100 = 9 9*4 = 36 ```

Question 29

2,200/25

Answer 29

``` 2,200/100 = 22 22*4 = 88 ```

Question 30

450/25

Answer 30

18

Question 31

750/25

Answer 31

30

Question 32

3,500/25

Answer 32

140

Question 33

6,000/25

Answer 33

240

Question 34

8,500/25

Answer 34

340

Question 35

725/25

Answer 35

29

Question 36

1,225/25

Answer 36

49

Question 37

4,500/25

Answer 37

180

Question 38

5,000/25

Answer 38

200

Question 39

3,000/25

Answer 39

120

Question 40

3200/25

Answer 40

128

Question 41

40,000/25

Answer 41

1,600

Question 42

65,000/25

Answer 42

650

Question 43

22,500/25

Answer 43

900

Question 44

7,400/25

Answer 44

296