Julian, Aubrey, Benjamin and Isaiah share the same hobby of collecting marbles. The average number of marbles collected by the 4 friends is 23. Aubrey collected 6 more marbles than Benjamin but 13 fewer marbles than Julian. Isaiah collected 5 marbles fewer than Benjamin. Find the average number of marbles collected by Aubrey and Isaiah. Round off your answer to the nearest whole number.
Number of marbles Benjamin collected = 1 u
Number of marbles Aubrey collected = 1 u + 6
Number of marbles Julian collected = 1 u + 6 + 13 = 1 u + 19
Number of marbles Isaiah collected = 1 u - 5

Total number of marbles collected
= 4 x 23
= 92

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

4 u + 20 = 92
4 u = 92 - 20 = 72

1 u = 72 ÷ 4 = 18

Total number of marbles collected by Aubrey and Isaiah
= 1 u + 6 + 1 u - 5
= 2 u + 1
= 2 x 18 + 1
= 37

Average number of marbles collected by Aubrey and Isaiah
= 37 ÷ 2
≈ 19 (Round off to the nearest whole number.)

Answer(s): 19