Jacob, Stella, Henry and Riordan share the same hobby of collecting marbles. The average number of marbles collected by the 4 friends is 28. Stella collected 9 more marbles than Henry but 16 fewer marbles than Jacob. Riordan collected 2 marbles fewer than Henry. Find the average number of marbles collected by Stella, Henry and Riordan. Round off your answer to the nearest whole number.
Number of marbles Henry collected = 1 u
Number of marbles Stella collected = 1 u + 9
Number of marbles Jacob collected = 1 u + 9 + 16 = 1 u + 25
Number of marbles Riordan collected = 1 u - 2

Total number of marbles collected
= 4 x 28
= 112

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

4 u + 32 = 112
4 u = 112 - 32 = 80

1 u = 80 ÷ 4 = 20

Total number of marbles collected by Stella, Henry and Riordan
= 1 u + 9 + 1 u + 1 u - 2
= 3 u + 7
= 3 x 20 + 7
= 67

Average number of marbles collected by Stella, Henry and Riordan
= 67 ÷ 3
≈ 22 (Round off to the nearest whole number.)

Answer(s): 22