Question

Three of four numbers have a sum of 17. If the average of the four numbers is 6, what is the fourth number?

Answer 1

1) 6 * 4 = 24 - a sum of four numbers
2) 24 - 17 = 7 - is the fourth number.

Answer 2

Answer: The fourth number is 7.

Explanation:

Sum of three numbers = 17

So, it becomes

`x_1+x_2+x_3=17`

Average of four numbers = 6

Since we know that formula for "Average":

`Average=(\sum x)/(n)\\\\6=(\sum x)/(4)\\\\24=\sum x`

`\sum x_i=24\\\\x_1+x_2+x_3+x_4=24\\\\17+x_4=24\\\\x_4=24-17\\\\x_4=7`

Hence, the fourth number is 7.