Noah, Elizabeth, Hannah and John share the same hobby of collecting erasers. The average number of erasers collected by the 4 friends is 21. Elizabeth collected 6 more erasers than Hannah but 13 fewer erasers than Noah. John collected 5 erasers fewer than Hannah. Find the average number of erasers collected by Elizabeth, Hannah and John. Round off your answer to the nearest whole number.
Number of erasers Hannah collected = 1 u
Number of erasers Elizabeth collected = 1 u + 6
Number of erasers Noah collected = 1 u + 6 + 13 = 1 u + 19
Number of erasers John collected = 1 u - 5

Total number of erasers collected
= 4 x 21
= 84

Total number of erasers collected in units
= 1 u + 1 u + 6 + 1 u + 19 + 1 u - 5
= 4 u + 20

4 u + 20 = 84
4 u = 84 - 20 = 64

1 u = 64 ÷ 4 = 16

Total number of erasers collected by Elizabeth, Hannah and John
= 1 u + 6 + 1 u + 1 u - 5
= 3 u + 1
= 3 x 16 + 1
= 49

Average number of erasers collected by Elizabeth, Hannah and John
= 49 ÷ 3
≈ 16 (Round off to the nearest whole number.)

Answer(s): 16