A. Multiply any number by 4
Example : 72 x 4 = 288
- Double the number being multiplied by four. (7 x 2 = 144)
- Double it again.(144 x 2 = 288)
B. Multiply any number by 5
Example : 27 x 5 = 135
- Divide the number being multiplied by 2. (27 / 2 = 13.5)
- Multiply step 1 by 10. (13.5 x 10 = 135)
C. Multiply any number by 9
Example : 52 x 9 = 468
- Multiply the number by 10. (52 x 10 = 520)
- Subtract the number from the result in step 1. (520 - 52 = 468)
D. Multiply any two digit number by 11
Example : 39 x 11 = 429
- Add together the digits of the number being multiplied by 11. ( 3 + 9 = 12)
- Place a zero between the two digits of the number being multiplied by 11. ( 309)
- Add the result from the step 1 to the zero in the number from step 2. Don't forget tocarry the 1 if there is one. (309 + 12 = 429)
E. Multiply any number by 25
Example : 44 x 25 = 1100
- Multiply the number by 100 (44 x 100 = 4400)
- Divide by 4 (4400 / 4 = 1100)
F. Multiply any number by 99
Example : 440 x 99 = 43560
- Multiply the number by 100 (440 x 100 = 44000)
- Subtract the number from the result in step 1 (44000 - 440 = 43560)
By : Stephanie Chungdinata
Source : Mathemagics
