Question

Cathy has taken two tests with scores of 80 and 90. To get an 80 average, what must her grade be on the third test?

A) 80
B) 85
C) 70
D) 75

Answer 1

Cathy needs to score a 70 on her third test to achieve an 80 average, as calculated by setting up the equation (80 + 90 + x) / 3 = 80 and solving for x.

Step-by-step explanation:

To calculate what grade Cathy needs on her third test to achieve an 80 average, you can set up an equation. Let's use x to represent the grade Cathy needs on the third test. The average of three numbers is the sum of those numbers divided by three. So, we need the equation (80 + 90 + x) / 3 = 80. Solving for x, we first multiply both sides by 3 to eliminate the denominator: 80 + 90 + x = 240. Next, we combine the known test scores: 170 + x = 240. Finally, we subtract 170 from both sides to solve for x: x = 240 - 170, which gives us x = 70.

Therefore, Cathy must score a 70 on her third test to achieve an 80 average. The correct answer is C) 70.