There are 10 students in a class. The average age of 9 of them is 8 years. By how many years will this average increase if the tenth student is (quite strangely) 28 years old?
Thoughts? Step-by-step reasoning:
9 students have an average age of 8 years so the sum of their ages is 9 * 8 = 72 years. A tenth student who is 28 years old will make the sum 72 + 28 = 100 years. The new average age will be 100 / 10 = 10 years. This is 10 - 8 = 2 years higher than the previous average.
Thus, the answer is 2.