Average help

Question

How do I do it step by step, 

Jim has gotten scores of 87 and 61 on his first two tests. What score must he get on his first three test to keep an average of 80 of greate. 

Answer 1

Let x = the score on Jim's 3rd test

 

87 + 61 + x  ≥ 80

         3

148 + x ≥ 240

x ≥ 92