math problem please help

Question

Sam had grades of 70, 81, and 77 on three tests. The final exam is worth as much as two tests. What grade must Sam get on the final to have an average of 85?

Answer 1

In this average problem, we see 3 examination scores of 70, 81, and 77.

We are told that the final examination is worth twice the regular scores.

There will be 5 exams, and the desired average is 85.

 

1. so, our equation becomes (70 + 81 +77 + 2x)/5 = 85

 

2. rearranging, 228 + 2x = 85 • 5, which becomes 2x = 425 - 228

 

3. solving for x, we 98.5

 

Proof: (70 + 81 +77 + 98.5 + 98.5)/5 = 425/5 = 85