How do I set up the following word problem?

Question

In order to earn an A in Chemistry class, Sandra must get an average of 90. There are four exams (each worth 100 points). Her first three exams grades are 88, 85 and 90. What is the minimum score that she must get on the fourth exam in order to receive an A in the Chemistry Course?

Answer 1

Average is the sum of the four tests grade divided by the total number of tests. 

 

(Test 1 + Test 2 + Test 3 + Test 4) / 4 = 90

Answer 2

f represents the score on the fourth exam

 

(88 + 85 + 90 + f) / 4 ≥ 90

 

Can you solve for f?

Answer 3

Let x = score on exam 4

 

Then, we want (88+85+90+x)/4 ≥ 90

 

                                263+x ≥ 360

 

                                       x ≥ 97

 

She needs at least a 97 on the fourth exam to guarantee a grade of "A".