Answer:
20 or 40 or 50
(there are many others)
Step-by-step explanation:
A counterexample is an example that shows the statement is not true. The statement in this question is that if a number is a multiple of 10 (10, 20, 30, 40, 50, 60...) then it is a multiple of 30. Some numbers are, like 60 and 90, but not all numbers. So for example (counterexample) 20 is a multiple of 10 but NOT a multiple of 30.
40 is a multiple of 10, but NOT a multople of 30.
50 is a multiple of 10, but NOT a multiple of 30.
