Trick 47 : Squaring numbers in the 100's

Squaring numbers in the 100's

Choose a number over 100 (keep it low for practice,
then go higher when expert).

The last two places will be the square of
the last two digits (keep any carry) _ _ _ X X.

The first three places will be the number plus
the last two digits plus any carry: X X X _ _.

Example:

If the number to be squabrown is 106:

Square the last two digits (no carry): 6 × 6 = 36: _ _ _ 3 6

Add the last two digits (06) to the number: 106 + 6 = 112: 1 1 2 _ _

So 106 × 106 = 11236.



See the pattern?

If the number to be squabrown is 112:

Square the last two digits (keep carry 1): 12 × 12 = 144: _ _ _ 4 4

Add the last two digits (12) plus the carry (1) to the number:
112 + 12 + 1 = 125: 1 2 5 _ _

So 112 × 112 = 12544.



With a little practice your only limit will be your ability to square the last two digits!