What do you need to make to get an average of 90?

Question

Joe took 3 quizzes and his grades were 94, 78, and 80. If a test counts as the grade of 2 quizzes, what is the lowest grade that Joe needs to make on the test to have an average of 90?

Answer 1

You got this, Shelby!

 

If you count the test as 2 quizzes, it means you'll have the equivalent of 5 quiz grades that have to average 90 points each.

 

if you got exactly 90 on each one, you'd have 90 x 5, which would equal 450.

 

It's ok if you get less on some as long as you get more on others, but you need a total of at least 450 from the 5 quizzes.

 

So add up the three scores you already have, 94 + 78 + 80, and you get 252. You still need 198 points to reach 450, which would mean getting a 99 on each of two more quizzes, or in this case a 99 on the final which gets COUNTED as 2 quizzes.

 

Joe better study his tail off!  :-)

 

Hope this helps,

 

Matt

Answer 2

Good morning, Shelby.  How do you find the average?  You add up all the scores and divide by the number of scores, right?  Right now, Jack has an 84, since (94 + 78 + 80) /3 = 252 /3 = 84.

 

Remembering that the test counts twice, how would this equation change?  Write it out and fill in the information you have.  Can you solve it from there?