David, Hazel, Isabella and Emily share the same hobby of collecting coins. The average number of coins collected by the 4 friends is 21. Hazel collected 9 more coins than Isabella but 16 fewer coins than David. Emily collected 2 coins fewer than Isabella. Find the average number of coins collected by Hazel, Isabella and Emily. Round off your answer to the nearest whole number.
Number of coins Isabella collected = 1 u
Number of coins Hazel collected = 1 u + 9
Number of coins David collected = 1 u + 9 + 16 = 1 u + 25
Number of coins Emily collected = 1 u - 2

Total number of coins collected
= 4 x 21
= 84

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

4 u + 32 = 84
4 u = 84 - 32 = 52

1 u = 52 ÷ 4 = 13

Total number of coins collected by Hazel, Isabella and Emily
= 1 u + 9 + 1 u + 1 u - 2
= 3 u + 7
= 3 x 13 + 7
= 46

Average number of coins collected by Hazel, Isabella and Emily
= 46 ÷ 3
≈ 15 (Round off to the nearest whole number.)

Answer(s): 15