Which of the following is a divisibility rule for 10?

• A. Ends in 0
• B. Ends in 5
• C. Is even
• D. Sum of digits is even

Answer: (A)

A number is divisible by 10 exactly when its last digit is 0. In base-10, having a last digit of 0 means the number can be written as 10 times an integer, so it has a factor of 10. Conversely, if a number is divisible by 10, its units digit must be 0.

The other patterns don’t guarantee divisibility by 10: ending in 5 means a factor of 5 but not necessarily 2; being even means a factor of 2 but not necessarily 5; and the sum of digits rule relates to divisibility by 3 or 9, not 10.