Question:
What is the average (arithmetic mean) of all the multiples of ten from 10 to 190 inclusive?

Option A):
110
Option B):
90
Option C):
100
Option D):
105

Correct Answer is Option C):
100

Explanation:
You could add up all the multiples of 10 (10 + 20 + 30 ....+190), and divide by the number of terms (19). Or you could realize that the average of an evenly spaced series of numbers is equal to the value of the middle term (or the average of the two middle terms if there are an even number of terms). The middle term out of 19 is the tenth term in the series = 100.