Anthony, Oliver, Aria and David share the same hobby of collecting erasers. The average number of erasers collected by the 4 friends is 27. Oliver collected 9 more erasers than Aria but 14 fewer erasers than Anthony. David collected 4 erasers fewer than Aria. Find the average number of erasers collected by Oliver and David. Round off your answer to the nearest whole number.
Number of erasers Aria collected = 1 u
Number of erasers Oliver collected = 1 u + 9
Number of erasers Anthony collected = 1 u + 9 + 14 = 1 u + 23
Number of erasers David collected = 1 u - 4

Total number of erasers collected
= 4 x 27
= 108

Total number of erasers collected in units
= 1 u + 1 u + 9 + 1 u + 23 + 1 u - 4
= 4 u + 28

4 u + 28 = 108
4 u = 108 - 28 = 80

1 u = 80 ÷ 4 = 20

Total number of erasers collected by Oliver and David
= 1 u + 9 + 1 u - 4
= 2 u + 5
= 2 x 20 + 5
= 45

Average number of erasers collected by Oliver and David
= 45 ÷ 2
≈ 23 (Round off to the nearest whole number.)

Answer(s): 23