Question

a group of four numbers has an average (arithmetic mean) of 13. the first three numbers are 10, 17, and 5. what is the other number? 20 18 17 15 13

Explanation:

Step1: Find sum of four numbers

$13\times4 = 52$

Step2: Find sum of first three numbers

$10 + 17+5=32$

Step3: Find fourth number

$52 - 32=20$

Answer:

20