2020 AMC 10A Problem 2

Problem 2 of 25EasierAlgebra

The numbers

3,

5,

7,

a,

and

b

have an average (arithmetic mean) of

15.

What is the average of

a

and

b?

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Solution

The five numbers have total sum

5\cdot15=75

. Since

3+5+7=15

, we have

a+b=75-15=60

, so the average of

a

and

b

30

. Thus, C is the correct answer.

Concepts: mean

Problem text and solution from the LIVE past-contest archive. See also the AoPS wiki page for community solutions.