Bob's Average?

Question

If Bob's grades in math class are a 65, 98, 80, and 87, and he wants an 80 average, what would he need to get on his next test 

Answer 1

Other tutors have used the typical procedure: (65+98+80+87+x)/5=80 which averages 5 numbers.

 

The needed score is x=5*80-(65+98+80+87), so you could just start there [ 5 tests; 80 is desired average, then, sum of 4 scores so far ].

 

x = 400-330

x=70

Answer 2

Average is the sum of the terms divided by the number of terms.  Right now, he has 4 grades.  When he adds another grade, his average will be 80.

 

Let x = the grade on next test

 

 

(65 + 98 + 80 + 87 + x) / 5 = 80

 

Solve for x.

 

(330 + x) / 5 = 80

 

 

Multiply both sides of the equation by 5.

 

330 + x = 400

 

 

Subtract 330 on both sides of the equation.

 

x = 70

 

 

He needs a score of 70 to get an average of 80.

Answer 3

(65+98+80+87+T)/5=80 where T=next test score

(330+T)/5=80

330+T=5*80

330+T=400

T=400-330

T=70