Amelia, Nathan, Julie and Lucy share the same hobby of collecting erasers. The average number of erasers collected by the 4 friends is 24. Nathan collected 9 more erasers than Julie but 16 fewer erasers than Amelia. Lucy collected 2 erasers fewer than Julie. Find the average number of erasers collected by Nathan and Lucy. Round off your answer to the nearest whole number.
Number of erasers Julie collected = 1 u
Number of erasers Nathan collected = 1 u + 9
Number of erasers Amelia collected = 1 u + 9 + 16 = 1 u + 25
Number of erasers Lucy collected = 1 u - 2

Total number of erasers collected
= 4 x 24
= 96

Total number of erasers collected in units
= 1 u + 1 u + 9 + 1 u + 25 + 1 u - 2
= 4 u + 32

4 u + 32 = 96
4 u = 96 - 32 = 64

1 u = 64 ÷ 4 = 16

Total number of erasers collected by Nathan and Lucy
= 1 u + 9 + 1 u - 2
= 2 u + 7
= 2 x 16 + 7
= 39

Average number of erasers collected by Nathan and Lucy
= 39 ÷ 2
≈ 20 (Round off to the nearest whole number.)

Answer(s): 20