what is a counterexample for the conjecture?
conjecture: any number that is divisible by 5 is also divisible by 10. (and if you can explain to me how to do this)

a. 32
b. 50
c. 25
d. 40

The Rule for 10: Numbers that are divisible by 10 need to be even and divisible by 5, because the prime factors of 10 are 5 and 2. Basically, this means that for a number to be divisible by 10, the last digit must be a 0. Take a look at the last digit: 23,890. The last digit is a 0.

Igot the answer of 15.8 years.