[ Decimal numeral system ]

Try to find all natural numbers that are 5 times larger than their last digit.

#
Think about what the last digit of the desired number could be.

## Solution

When multiplied by 5, the last digit did not change, so it must have been 0 or 5. If the last digit was 0, then the entire number would be 0, but we are looking for natural numbers. Therefore, the last digit must have been 5. And the entire number is 25. Naturally, the number cannot be greater than 25, since it is 5 times the digit, i.e., it cannot exceed 45.

## Answer

25.