Squaring a 2-digit number ending in 5

1. Choose a 2-digit number ending in 5.
2. Multiply the first digit by the next consecutive number.
3. The product is the first two digits: XX _ _.
4. The last part of the answer is always 25: _ _ 2 5.

Example:

1. If the number is 35, 3 × 4 = 12 (first digit
   times next number). 1 2 _ _
2. The last part of the answer is always 25: _ _ 2 5.
3. So 35 × 35 = 1225.

See the pattern?

1. For 65 × 65, 6 × 7 = 42 (first digit
   times next number): 4 2 _ _.
2. The last part of the answer is always 25: _ _ 2 5.
3. So 65 × 65 = 4225.

Posted in: Mathematics Tips,Squaring Numbers,Tricky mathematics