How to find overall average?? help please

Question

Bruce scored a 12, 18, 16, and 17 on his first four quizzes. What must his score on the fifth quiz be if he wants an overall average of 16?

Answer 1

Hello Jane,

 

There are two different ways to figure out the answer to this problem.

The first way to do this is to take the scores Bruce received on his first four quizzes and see how they compare to the desired average (16):

 

12 is 4 less than 16 (-4)

18 is 2 more than 16 (+2)

16 is equal to 16 (0)

17 is 1 more than 16 (+1)

 

Now, lets add up all of those plusses and minuses (-4+2+0+1= -1)

Since Bruce is one point short of having an average of 16, we need to add that point to his next quiz's score. 

 

Bruce needs to score 17 on his last quiz.

 

Another way we can figure out this problem is to multiply 16*5=80, which is the sum total of 5 quizzes with an average of 16.

Next, we add up the known totals of the 4 previous quizzes (12+18+16+17=63). Lastly, we subtract this total from the average sum total (80-63=17).

 

Again, Bruce needs to score 17 on his last quiz.