Squares Ending in 5 Trick

Any number ending in 5, when squared, will have a result that ends in 25. The preceding digits can be found by taking the leading digit(s) and multiplying by one greater than itself.

The formula is derived from $(10a+5)^2 = 100a^2 + 100a + 25 = 100a(a+1) + 25$.

For example, to calculate $85^2$:

• Last two digits: 25
• Preceding digits: $8 \times (8+1) = 72$

The result is 7225.