What is the average of the first 15 odd numbers?

The first 15 odd numbers are 1, 3, 5, ..., 29. They are evenly spaced, so their average is the middle one, the 8th, which is 15. (The sum is $15\times 15=225$ and 225/15 = 15.) 16 is the average of the first 15 EVEN numbers, which is $n+1$. 8 is the average of the first 15 NATURAL numbers, which is $(n+1)/2$. 29 is the last odd number itself, not the average.