Emily, Alexander, Lucas and Jonathan share the same hobby of collecting cards. The average number of cards collected by the 4 friends is 25. Alexander collected 7 more cards than Lucas but 16 fewer cards than Emily. Jonathan collected 2 cards fewer than Lucas. Find the average number of cards collected by Alexander, Lucas and Jonathan. Round off your answer to the nearest whole number.
Number of cards Lucas collected = 1 u
Number of cards Alexander collected = 1 u + 7
Number of cards Emily collected = 1 u + 7 + 16 = 1 u + 23
Number of cards Jonathan collected = 1 u - 2

Total number of cards collected
= 4 x 25
= 100

Total number of cards collected in units
= 1 u + 1 u + 7 + 1 u + 23 + 1 u - 2
= 4 u + 28

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

1 u = 72 ÷ 4 = 18

Total number of cards collected by Alexander, Lucas and Jonathan
= 1 u + 7 + 1 u + 1 u - 2
= 3 u + 5
= 3 x 18 + 5
= 59

Average number of cards collected by Alexander, Lucas and Jonathan
= 59 ÷ 3
≈ 20 (Round off to the nearest whole number.)

Answer(s): 20