11 times any digit number
Take any number you want to multiply by 11, like 18 for example
Write 18 then shift 18 one left space over:
18
18
And add the numbers up in the middle column to get 198 as the sum. 1 (1+8 = 9) 8
If it is a double digit number like 88, where it's:
88
88
Then add the middle 8s to be 16, and carry the 1 over to the left for:
968
11 times any two-digiter
To multiply, say, 11 x 32, add the digits of 32 (3 + 2 = 5) and insert the sum between them: 352. Numbers with two-digit sums use a slight variation: For 11 x 84 (8 + 4 = 12), add the 1 from 12 to the 8 and leave the 2 in the middle: 924.
18
And add the numbers up in the middle column to get 198 as the sum. 1 (1+8 = 9) 8
If it is a double digit number like 88, where it's:
88
88
Then add the middle 8s to be 16, and carry the 1 over to the left for:
968
11 times any two-digiter
To multiply, say, 11 x 32, add the digits of 32 (3 + 2 = 5) and insert the sum between them: 352. Numbers with two-digit sums use a slight variation: For 11 x 84 (8 + 4 = 12), add the 1 from 12 to the 8 and leave the 2 in the middle: 924.
To find the square of the next number in a series without multiplying: Say you know the square of 12 is 144. Add 12 to 144 and add the next number — in this case, 13 — to find the square of 13: 144 + 12 = 156 + 13 = 169, the square of 13; and then, 169 + 13 = 182 + 14 = 196, etc.
Magic number
Ask a fan to think of any number. Then have them double it, add 12, divide by 2, and subtract the original number. Before they're done, tell them the answer: 6. It will always be 6.
Fives Times
If you have a multiplication of five, then an easy way to find the answer is to half the multiplied number and times by ten.
For example: 24 * 5 = (24 / 2) * 10 = 120
Ask a fan to think of any number. Then have them double it, add 12, divide by 2, and subtract the original number. Before they're done, tell them the answer: 6. It will always be 6.
Fives Times
If you have a multiplication of five, then an easy way to find the answer is to half the multiplied number and times by ten.
For example: 24 * 5 = (24 / 2) * 10 = 120
Squaring Numbers that End in Five
To square a number that ends in 5 (e.g., 25, 65, 1005) simply remove the 5 from the end of the number and multiply the remaining number times the next number then tack a '25' on the end of it (squares of numbers that end in 5 will always end in 25).
To square a number that ends in 5 (e.g., 25, 65, 1005) simply remove the 5 from the end of the number and multiply the remaining number times the next number then tack a '25' on the end of it (squares of numbers that end in 5 will always end in 25).
For example,
25 squared is 2*3 = 6 and tack on '25' to the end = 625.
65 squared is 6*7 = 42 and tack on '25; to the end = 4225.
Easy way to learn square of some numbers
-13^2= 169, while 31^2= 961, it would seem every number (except the exponent) is visually flipped.
-14^2= 196, while 41^2= 1681, this may seem somewhat of a stretch, but imagine 196 as 18(16), where 16 is one decimal place. The principle above applies
Dividing by 5
Dividing a large number by five is actually very simple. All you do is multiply by 2 and move the decimal point:
For example- 32/5 = (32*2)/10 = 64/10 = 6.4
Subtracting trick
For example:- 89-64 = (89+1)-(64+1) = 90-65 = 25
