Linear word problem

Question

On her first four 100-point tests, Li received grades of 78, 85, 95, and 96. If she wants to have at least a 90 average in the class, what is the lowest score she can receive on her last 100-point test? (rounding is not considered)

Answer 1

Hello, thank you for taking the time to post your question!

The underlying equation that we want to solve on this one is

(78 + 85 + 95 + 96 + x) / 5 = 90     because she needs the average across all 5 tests to be 90

Solving that algebraically for the value of “x” yields

354 + x = 450

x = 450 – 354 = 96

meaning that the lowest score Li can receive on her last test to hit these criteria is 96

I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)

Answer 2

In order to have a 90 average on 5 tests, you need a total of 450 points, because 90*5=450. So add up the points she has so far (354). On the last test she needs to get 96 to bring the total to 450.