Squaring numbers ending in 5

To square any number that ends in 5, simply

1. Multiply the ten's (left) digit(s) by the next higher digit (itself+1)
2. Attach 25 at the end

Example: If the number to be squared is 35;

Notice, the first digit is 3, and the next higher number to 3 is 4.

So, the first part of the answer is 3 × 4 = 12 (first digit multiplied by next higher digit). And the last part of the answer is always 25.

So, 35² = 1225

Similarly, 75² = 5625

The answer is in two parts: The first part is the first number; which is 7, multiplied by the next higher number that is 8; giving (7 x 8 =) 56. The last part is always 25, giving the final answer 5625.

65² = 4225
95² = 9025 

We can also square 3-digit numbers this way, by starting with the first two digits:

Example:      125² =?

a.  First part is 12 × 13 = 156

b.  The last part is 25.

So, 125² = 15,625

Similarly, 995² = 99 × 100 = 9900 and 25; that is 990025.