Ethan, Leah, Owen and Luke share the same hobby of collecting pens. The average number of pens collected by the 4 friends is 20. Leah collected 7 more pens than Owen but 12 fewer pens than Ethan. Luke collected 2 pens fewer than Owen. Find the average number of pens collected by Leah and Luke. Round off your answer to the nearest whole number.
Number of pens Owen collected = 1 u
Number of pens Leah collected = 1 u + 7
Number of pens Ethan collected = 1 u + 7 + 12 = 1 u + 19
Number of pens Luke collected = 1 u - 2

Total number of pens collected
= 4 x 20
= 80

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

4 u + 24 = 80
4 u = 80 - 24 = 56

1 u = 56 ÷ 4 = 14

Total number of pens collected by Leah and Luke
= 1 u + 7 + 1 u - 2
= 2 u + 5
= 2 x 14 + 5
= 33

Average number of pens collected by Leah and Luke
= 33 ÷ 2
≈ 17 (Round off to the nearest whole number.)

Answer(s): 17