A student on her first 3 tests receive an average score of N points

A student on her first 3 tests receive an average score of N points. If she exceeds her previous average score by 20 points on her fourth test, then what is the average score for the first 4 tests?

  1. N + 10 
  2. N + 4
  3. N + 5 
  4. N + 20

Answer

Total score for 3 tests = 3N

Score in 4th test = N+20

Total score for 4 tests = 3N+N+20 = 4N+20

Average of 4 tests = (4N+20)/4 = N+5

20 points are increased in fourth test, so new average will be increased by 20/4 = 5.

The correct option is C.