FastMath Practice Flashcards
1
Q
How to multiply by 25
A
Divide by 4 then multiply by 100
2
Q
How to divide numbers with multiples of 4 by 4?
A
Left to right, digit by digit. Ex: 84/4 –> 8/4 = 2 and 4/4 = 1, concatenate to 21
3
Q
How to divide numbers with non-multiples of 4 by 4?
I.e. 52/4
A
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
4
Q
8*25
A
8÷ 4 = 2
2 *100 = 200
5
Q
25*55
A
44 ÷ 4 =11
11*100 =1,100
6
Q
16*25
A
16/4 = 4 4*100 = 400
7
Q
25*40
A
40/4 = 10 10*100 = 1000
8
Q
24*25
A
24/4 = 6 6*100 = 600
9
Q
25*60
A
60/4 = 15 15*100 = 1500
10
Q
320 * 25
A
320/4 = 80 80*100 = 8000
11
Q
25*18
A
450
12
Q
26*25
A
26/4 = 6.5 –> 6.5*100=
650
13
Q
25*9
A
9/4 = 2.25 –> * 100 = 225
14
Q
17*25
A
425
15
Q
25*900
A
22,500
16
Q
25*800
A
20,000
17
Q
160*25
A
4,000
18
Q
1,200*25
A
30,000
19
Q
25*140
A
140/2 = 70 70/2 = 35 35*100 = 3,500
20
Q
860*25
A
860/2 = 430
430/2 = 215
*100
21,500
21
Q
25*124
A
3100
22
Q
180*25
A
4,500
23
Q
25*328
A
8,200
24
Q
How to divide by 25
A
25 = 100/4, so
- Multiply by 4 (or multiply by 2 twice) and then divide by 100
OR - Divide by 100 and then multiply by 4
25
300/25
```
300/100 = 3
3*4 = 12
```
OR 300*4 = 1200
1200/100 = 12
26
700/25
```
700/100 = 7
7*4 = 28
```
27
1,200/25
```
1,200/100 = 12
12*4 = 48
```
28
900/25
```
900/100 = 9
9*4 = 36
```
29
2,200/25
```
2,200/100 = 22
22*4 = 88
```
30
450/25
18
31
750/25
30
32
3,500/25
140
33
6,000/25
240
34
8,500/25
340
35
725/25
29
36
1,225/25
49
37
4,500/25
180
38
5,000/25
200
39
3,000/25
120
40
3200/25
128
41
40,000/25
1,600
42
65,000/25
650
43
22,500/25
900
44
7,400/25
296
