Riordan, Lilian, Jackson and Luke share the same hobby of collecting stickers. The average number of stickers collected by the 4 friends is 29. Lilian collected 9 more stickers than Jackson but 16 fewer stickers than Riordan. Luke collected 2 stickers fewer than Jackson. Find the average number of stickers collected by Lilian and Luke. Round off your answer to the nearest whole number.
Number of stickers Jackson collected = 1 u
Number of stickers Lilian collected = 1 u + 9
Number of stickers Riordan collected = 1 u + 9 + 16 = 1 u + 25
Number of stickers Luke collected = 1 u - 2

Total number of stickers collected
= 4 x 29
= 116

Total number of stickers collected in units
= 1 u + 1 u + 9 + 1 u + 25 + 1 u - 2
= 4 u + 32

4 u + 32 = 116
4 u = 116 - 32 = 84

1 u = 84 ÷ 4 = 21

Total number of stickers collected by Lilian and Luke
= 1 u + 9 + 1 u - 2
= 2 u + 7
= 2 x 21 + 7
= 49

Average number of stickers collected by Lilian and Luke
= 49 ÷ 2
≈ 25 (Round off to the nearest whole number.)

Answer(s): 25