8. To find an average, you add all the numbers together and then divide by how many numbers there are. Since we're trying to find the last number, we'll set up the problem like this:
(72+82+82+x)/4 = 80
Add your numbers: (286+x)/4 = 80
Divide each side by 4: 286+x = 320
Subtract 286 from 320: x = 34
He needs to get a 34 on his last test for an 80 average.
9. We want to find the total of his first 5 scores, so we multiply 100 by 5 to get 500.
Add 118 to 500: 618
Divide by 6 (the new number of bowling scores): 103
His new average is 103.
