tell me a tricks for multiplication
Answers
Do it in a copy or by brain
2
add the number to itself (in other words, double it)
Example 2×9 = 9+9 = 18
4
double, then double again
Example 4×9: double 9 is 18, double 18 is 36
5
Cut in half, then times 10
Example: 5x6: Cut 6 in half to get 3, then times 10 for 30
Or times 10 then cut in half
Example: 5x9: 9 times 10 is 90, then cut in half for 45
Also the last digit goes 5, 0, 5, 0, ... like this: 5, 10, 15, 20, ...
6
when you multiply 6 by an even number, they both end in the same digit.
Examples: 6×2=12, 6×4=24, 6×6=36, etc
7×8
Think "5,6,7,8": 56=7×8
8
Double, double, double!
Example: 8×6: double 6 is 12, double 12 is 24, double 24 is 48
9
is 10× the number minus the number.
Example: 9×6 = 10×6−6 = 60−6 = 54
the ones digit goes 9, 8, 7, 6, ...: 9, 18, 27, 36, 45, ...
the tens digit goes 0, 1, 2, 3, ...: 9, 18, 27, 36, 45, ...
subtract one to get the tens digit, and the tens and ones digit together make 9
Example: 9×5: tens digit is 4, 4 and 5 make 9, so 45
Example: 9×8: tens digit is 7, 7 and 2 make 9, so 72
fingers multiply 9
your hands can help! Example: to multiply 9 by 8, hold your 8th finger down, and count "7" and "2", the answer is 72
10
put a zero after it
Example: 10×2 = 20
11
up to 11x9: just repeat the digit. Example: 11x4 = 44
for 11×10 to 11×18: write the sum of the digits between the digits
Example: 11×15 = 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 the one". Example: 11×75 = 7(7+5)5 = 7(12)5 = 825.
12
is 10× plus 2×
Example: 12×4 = 40+8 = 48
15
multiply by 10, then add half again
Example: 15×4 = 40+20 = 60
Example: 15×9 = 90+45 = 135
20
multiply by 10, then double
Example: 20×4 = 40+40 = 80
Example: 20×7 = 70+70 = 140
Hope it helps