math ( average)
posted by sasha .
a student wants to get an average of 80 on the 5 tests to earn an A grade.on the 4 test he gets 79, 88,64,78. how much should he score on the 5th test so that he gets this average of 80?

(79+88+64+78+newtest)/5 = 80
solve for "newtest" 
still don't get it

Check my answer below.

Let's say the score of the 5th test her is x. To get an average of something, you add everything up and divide by the number of numbers (in this case, tests), right? So, this is how you would set this one up:
79+88+64+78+x
 = 80
5
Can you solve the rest? 
The student needs a total of 400 points on 5 tests to get an average of 80.
He has a total of 309 on the first four tests. What score does he need on the fifth test to bring his total up to 400? 
91

What is the next step after adding and dividing?