Lucas, Ethan, Tommy and Aubrey share the same hobby of collecting marbles. The average number of marbles collected by the 4 friends is 24. Ethan collected 6 more marbles than Tommy but 13 fewer marbles than Lucas. Aubrey collected 5 marbles fewer than Tommy. Find the average number of marbles collected by Ethan and Aubrey. Round off your answer to the nearest whole number.
Number of marbles Tommy collected = 1 u
Number of marbles Ethan collected = 1 u + 6
Number of marbles Lucas collected = 1 u + 6 + 13 = 1 u + 19
Number of marbles Aubrey collected = 1 u - 5

Total number of marbles collected
= 4 x 24
= 96

Total number of marbles collected in units
= 1 u + 1 u + 6 + 1 u + 19 + 1 u - 5
= 4 u + 20

4 u + 20 = 96
4 u = 96 - 20 = 76

1 u = 76 ÷ 4 = 19

Total number of marbles collected by Ethan and Aubrey
= 1 u + 6 + 1 u - 5
= 2 u + 1
= 2 x 19 + 1
= 39

Average number of marbles collected by Ethan and Aubrey
= 39 ÷ 2
≈ 20 (Round off to the nearest whole number.)

Answer(s): 20