John, Riordan, Hannah and Noah share the same hobby of collecting pens. The average number of pens collected by the 4 friends is 25. Riordan collected 9 more pens than Hannah but 15 fewer pens than John. Noah collected 5 pens fewer than Hannah. Find the average number of pens collected by Riordan, Hannah and Noah. Round off your answer to the nearest whole number.
Number of pens Hannah collected = 1 u
Number of pens Riordan collected = 1 u + 9
Number of pens John collected = 1 u + 9 + 15 = 1 u + 24
Number of pens Noah collected = 1 u - 5

Total number of pens collected
= 4 x 25
= 100

Total number of pens collected in units
= 1 u + 1 u + 9 + 1 u + 24 + 1 u - 5
= 4 u + 28

4 u + 28 = 100
4 u = 100 - 28 = 72

1 u = 72 ÷ 4 = 18

Total number of pens collected by Riordan, Hannah and Noah
= 1 u + 9 + 1 u + 1 u - 5
= 3 u + 4
= 3 x 18 + 4
= 58

Average number of pens collected by Riordan, Hannah and Noah
= 58 ÷ 3
≈ 19 (Round off to the nearest whole number.)

Answer(s): 19