Ryan, Gabriel, Lucy and Lily share the same hobby of collecting erasers. The average number of erasers collected by the 4 friends is 25. Gabriel collected 8 more erasers than Lucy but 13 fewer erasers than Ryan. Lily collected 5 erasers fewer than Lucy. Find the average number of erasers collected by Gabriel and Lily. Round off your answer to the nearest whole number.
Number of erasers Lucy collected = 1 u
Number of erasers Gabriel collected = 1 u + 8
Number of erasers Ryan collected = 1 u + 8 + 13 = 1 u + 21
Number of erasers Lily collected = 1 u - 5

Total number of erasers collected
= 4 x 25
= 100

Total number of erasers collected in units
= 1 u + 1 u + 8 + 1 u + 21 + 1 u - 5
= 4 u + 24

4 u + 24 = 100
4 u = 100 - 24 = 76

1 u = 76 ÷ 4 = 19

Total number of erasers collected by Gabriel and Lily
= 1 u + 8 + 1 u - 5
= 2 u + 3
= 2 x 19 + 3
= 41

Average number of erasers collected by Gabriel and Lily
= 41 ÷ 2
≈ 21 (Round off to the nearest whole number.)

Answer(s): 21