The average of 3 numbers is 7. two of the numbers are 8 and 9. what is the third?

(8+9+x) / 3=7

(17+x) = 21

x=4

Make an equation. x will be the third number.

To find the average, you add up the numbers then divide the sum by the number of numbers you added up.

(8 + 9 + x) : 3 = 7

Now solve. Add up like terms (8 + 9).

(17 + x) : 3 = 7

Multiply both sides by 3.

17 + x = 21

Subtract both sides by 17.

x = 4

The third number is 4.