Question

If m, n are natural numbers, for what values of m, does 2ⁿ × 5^m ends in 5?

Answer 1

2ⁿ × 5^m

2ⁿ is always even for all values of n.

5^m is always odd and ends with 5 for all values of m.

But 2ⁿ × 5^m is always even and ends in 0.

∴ 2ⁿ × 5^m cannot end with the digit 5 for any values of m.

No value of m will satisfy 2ⁿ × 5^m ends in 5.