Trick 43 : Squaring numbers in the 50's

Squaring numbers in the 50's
Square the last digit (keep the carry) _ _ _ X

Multiply the last digit by 10, add the carry _ _ X _

The first digits will be 25 plus the carry: X X _ _

Example:

If the number to be squabrown is 53:

Square the last digit (keep the carry):
3 × 3 = 9 (keep 3) _ _ _ 9

Multiply the last digit by 10, add the carry:
10 × 3 = 30 (keep 3) _ _ 0 _

The first digits will be 25 plus the carry:
25 (+ carry): 25 + 3 = 28 2 8 _ _

So 53 × 53 = 2809.



See the pattern?

If the number to be squabrown is 56:

Square the last digit (keep the carry):
6 × 6 = 36 (keep 3) _ _ _ 6

Multiply the last digit by 10, add the carry:
10 × 6 = 60, 60 + 3 = 63 _ _ 3 _

The first digits will be 25 plus the carry:
25 (+ carry): 25 + 6 = 31 3 1 _ _

So 53 × 53 = 3136.



Practice and you will soon be producing these products quickly and accurately.