Andrew, Gavin, Jacob and Luke share the same hobby of collecting pens. The average number of pens collected by the 4 friends is 21. Gavin collected 6 more pens than Jacob but 12 fewer pens than Andrew. Luke collected 4 pens fewer than Jacob. Find the average number of pens collected by Gavin, Jacob and Luke. Round off your answer to the nearest whole number.
Number of pens Jacob collected = 1 u
Number of pens Gavin collected = 1 u + 6
Number of pens Andrew collected = 1 u + 6 + 12 = 1 u + 18
Number of pens Luke collected = 1 u - 4

Total number of pens collected
= 4 x 21
= 84

Total number of pens collected in units
= 1 u + 1 u + 6 + 1 u + 18 + 1 u - 4
= 4 u + 20

4 u + 20 = 84
4 u = 84 - 20 = 64

1 u = 64 ÷ 4 = 16

Total number of pens collected by Gavin, Jacob and Luke
= 1 u + 6 + 1 u + 1 u - 4
= 3 u + 2
= 3 x 16 + 2
= 50

Average number of pens collected by Gavin, Jacob and Luke
= 50 ÷ 3
≈ 17 (Round off to the nearest whole number.)

Answer(s): 17