Question

Find a counterexample to show that the following statement is false.

The sum of three multiples of 5 will always end in a 5.

Answer 1

5 + 10 + 15 = 30

Explanation:

You want a sum of three multiples of 5 that does not end in 5.

Multiples of 5

Any odd multiple of 5 will end in 5. An even multiple will not.

In order for the sum to not end in 5, the total of the multipliers must be even:

1×5 +2×5 +3×5 = 6×5 = 30

5 +10 +15 = 30 . . . . . . three multiples of 5 whose sum does not end in 5