The average (arithmetic mean) of four numbers is 4a + 16. when a fifth number is added, the average becomes 5a + 20. the fifth number is

a. a - 4
b. a + 4
c. 4a + 4
d. 4a + 16
e. 9a + 36

Step-by-step explanation:

The average (arithmetic mean) of four numbers is 4a + 16. When a fifth number is added, the average becomes 5a + 20.

The average (arithmetic mean) of four numbers is 4a + 16.

Sum of 4 numbers = 4 times the average

Sum of 4 numbers =

sum  of 5 numbers = 5 times the average of 5 numbers

Sum of 5 numbers =

fifth number = sum of 5 numbers minus the sum of 4 numbers

i think the answer is b

combine all like terms then its just a 2 step equation