I'm studying for a math contest and not understanding some problems and the answers for them. Here are a few questions and what I don't understand about them:

Which of the following sets of whole numbers has the largest average?

(A)Multiples of 2 between 1 and 101. (B) Multiples of 3 between 1 and 101. (C) Multiples of 4 between 1 and 101. (D) Multiples of 5 between 1 and 101. (E) Multiples of 6 between 1 and 101

I'd think the answer would be E, but the answer key says that it is D. Any input?

The mean, median, unique mode, and range of a collection of eight integers are all equal to 8. the largest integer that can be an element in this collection is:

(A) 11. (B) 12. (C) 13. (D) 14. (E) 15.

I'm not entirely sure what a 'unique mode' is.

I'm fairly certain the highest number could be anything, because the lowest numbers could bring down the average. Their answer is D.

Thanks in advance!