Shelly's scores on her first two tests in Algebra were 72 and 89. What will she need to make on the third test to have an average of at least 80?

79 or better

80 or better

87 or better

95 or better

Question

Shelly's scores on her first two tests in Algebra were 72 and 89. What will she need to make on the third test to have an average of at least 80?
 
		
79 or better
 		
80 or better
 		
87 or better
 		
95 or better

australopithecus · Answer

Just use the formula for averages
(x/number of results)*100 = average

we know she wrote 3 tests so we divide by 3 we know the scores of two of the tests, we do not know the score for the third test so it is our variable x in the formula
we also know she wants an 80% thus we set the formula for averages equal to 80

((0.72 + 0.89 + x)/3)*100 = 80

australopithecus · Answer

79 or better

australopithecus · Answer

if you solved for x you would see x=79

australopithecus · Answer

https://www.wolframalpha.com/input/?i=%28%280.72+%2B+0.89+%2B+x%29%2F3%29*100+%3D+80

anonymous · Answer

The answer is 79, because if you add 72, 79, and 89, you get 240. Divide that by 3 and you get 80. Therefore, she will have an average of 80. A is the answer.