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