Question

you have a list of 7 numbers. the average of the numbers is 9. if you take away one of the numbers, the average of the numbers is 8. what number did you take away?

Answer 1

There was a 15 among the 7 numbers. That is the number you removed.

Explanation:

x/7 = 9 (1)

(x - y)/6 = 8 (2)

Multiply 1 by 7

x/7 * 7 = 9*7

x = 63

Put 63 for x into equation 2

(63 - y)/6 = 8 Multiply by 6

6*(63-y)/6 =8*6

63 - y = 48 Add y to both sides

63-y+y = 48+y

63 = 48 + y Subtract 48 from both sides

63-48=48-48+y

y = 15