Trick 31 : Squaring a 2-digit number ending in 5

Squaring a 2-digit number ending in 5
Choose a 2-digit number ending in 5.

Multiply the first digit by the next consecutive number.

The product is the first two digits: XX _ _.

The last part of the answer is always 25: _ _ 2 5.

Example:

If the number is 35, 3 × 4 = 12 (first digit
times next number). 1 2 _ _

The last part of the answer is always 25: _ _ 2 5.

So 35 × 35 = 1225.



See the pattern?

For 65 × 65, 6 × 7 = 42 (first digit
times next number): 4 2 _ _.

The last part of the answer is always 25: _ _ 2 5.

So 65 × 65 = 4225.