Zoey, Victoria, Christian and Luke share the same hobby of collecting marbles. The average number of marbles collected by the 4 friends is 23. Victoria collected 7 more marbles than Christian but 12 fewer marbles than Zoey. Luke collected 2 marbles fewer than Christian. Find the average number of marbles collected by Victoria and Luke. Round off your answer to the nearest whole number.
Number of marbles Christian collected = 1 u
Number of marbles Victoria collected = 1 u + 7
Number of marbles Zoey collected = 1 u + 7 + 12 = 1 u + 19
Number of marbles Luke collected = 1 u - 2

Total number of marbles collected
= 4 x 23
= 92

Total number of marbles collected in units
= 1 u + 1 u + 7 + 1 u + 19 + 1 u - 2
= 4 u + 24

4 u + 24 = 92
4 u = 92 - 24 = 68

1 u = 68 ÷ 4 = 17

Total number of marbles collected by Victoria and Luke
= 1 u + 7 + 1 u - 2
= 2 u + 5
= 2 x 17 + 5
= 39

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

Answer(s): 20