Christopher, Evelyn, Elizabeth and Jonathan share the same hobby of collecting coins. The average number of coins collected by the 4 friends is 21. Evelyn collected 8 more coins than Elizabeth but 13 fewer coins than Christopher. Jonathan collected 5 coins fewer than Elizabeth. Find the average number of coins collected by Evelyn and Jonathan. Round off your answer to the nearest whole number.
Number of coins Elizabeth collected = 1 u
Number of coins Evelyn collected = 1 u + 8
Number of coins Christopher collected = 1 u + 8 + 13 = 1 u + 21
Number of coins Jonathan collected = 1 u - 5

Total number of coins collected
= 4 x 21
= 84

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

4 u + 24 = 84
4 u = 84 - 24 = 60

1 u = 60 ÷ 4 = 15

Total number of coins collected by Evelyn and Jonathan
= 1 u + 8 + 1 u - 5
= 2 u + 3
= 2 x 15 + 3
= 33

Average number of coins collected by Evelyn and Jonathan
= 33 ÷ 2
≈ 17 (Round off to the nearest whole number.)

Answer(s): 17