Christian, Sebastian, Josiah and Alexander share the same hobby of collecting marbles. The average number of marbles collected by the 4 friends is 30. Sebastian collected 9 more marbles than Josiah but 14 fewer marbles than Christian. Alexander collected 4 marbles fewer than Josiah. Find the average number of marbles collected by Sebastian and Alexander. Round off your answer to the nearest whole number.
Number of marbles Josiah collected = 1 u
Number of marbles Sebastian collected = 1 u + 9
Number of marbles Christian collected = 1 u + 9 + 14 = 1 u + 23
Number of marbles Alexander collected = 1 u - 4

Total number of marbles collected
= 4 x 30
= 120

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

4 u + 28 = 120
4 u = 120 - 28 = 92

1 u = 92 ÷ 4 = 23

Total number of marbles collected by Sebastian and Alexander
= 1 u + 9 + 1 u - 4
= 2 u + 5
= 2 x 23 + 5
= 51

Average number of marbles collected by Sebastian and Alexander
= 51 ÷ 2
≈ 26 (Round off to the nearest whole number.)

Answer(s): 26