Question 238907
Hello, 
To find the average of numbers, we need to add all the numbers and divide by 5. 
Since one of the numbers is unknown we'll represent by x so the equation will be:
(84+82+81+79+x)/5 = 84  Combine like terms gives us:
(326+x)/5 = 84  Multiply both sides by 5
326 + x = 420  Subtract both sides by 326 gives us:
x = 94 There you go, he needs a 94 on the test to have an average of 84.
RJ Toftness
www.math-unlock.com