MATH'S TIPS AND TRICK
Tricks by Number
to multiply
by | Trick |
|---|---|
2
| add the number to itself (example 2×9 = 9+9) |
5
| the last digit goes 5, 0, 5, 0, ... |
| is always half of 10× (Example: 5x6 = half of 10x6 = half of 60 = 30) | |
| is half the number times 10 (Example: 5x6 = 10x3 = 30) | |
6
| when you multiply 6 by an even number, they both end in the same digit. Example: 6×2=12, 6×4=24, 6×6=36, etc |
9
| 
the last digit goes 9, 8, 7, 6, ...
your hands can help! Example: to multiply 9 by 8, hold your 8th finger down, and count "7" and "2", the answer is 72 |
| is 10× the number minus the number. Example: 9×6 = 10×6−6 = 60−6 = 54 | |
| when you add the answer's digits together, you get 9. Example: 9×5=45 and 4+5=9. (But not with 9×11=99) | |
10
| put a zero after it |
11
| up to 9x11: just repeat the digit (Example: 4x11 = 44) |
| for 10x11 to 18x11: write the sum of the digits between the digits Example: 15x11 = 1(1+5)5 = 165 Note: this works for any two-digit number, but when the sum of the digits is more than 9, we need to CARRY ONE. Example: 75x11 = 7(7+5)5 = 7(12)5 = 825. | |
12
| is 10× plus 2× |
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