Question

On four exams, Wallace’s grades were 79,93,91, and 68. What grade must he obtain on his fifth exam to have an 80 average?

Answer 1

(79 + 93 + 91 + 68 + x) / 5 = 80
(331 + x) / 5 = 80.....multiply both sides by 5
331 + x = 80 * 5
331 + x = 400
x = 400 - 331
x = 69 <=== he would have to make at least a 69

Answer 2

(79 + 93 + 91 + 68 + x) / 5 = 80

Simplify

(331 + x)/5 = 80

Multiply 5 to both sides to isolate the x.

331 + x = 400

Isolate the x. Subtract 331 from both sides

x + 331 (-331) = 400 (-331)

x = 69

69 is your answer

hope this helps