Nathan, Michael, Luke and Robert share the same hobby of collecting buttons. The average number of buttons collected by the 4 friends is 24. Michael collected 7 more buttons than Luke but 12 fewer buttons than Nathan. Robert collected 2 buttons fewer than Luke. Find the average number of buttons collected by Michael, Luke and Robert. Round off your answer to the nearest whole number.
Number of buttons Luke collected = 1 u
Number of buttons Michael collected = 1 u + 7
Number of buttons Nathan collected = 1 u + 7 + 12 = 1 u + 19
Number of buttons Robert collected = 1 u - 2

Total number of buttons collected
= 4 x 24
= 96

Total number of buttons collected in units
= 1 u + 1 u + 7 + 1 u + 19 + 1 u - 2
= 4 u + 24

4 u + 24 = 96
4 u = 96 - 24 = 72

1 u = 72 ÷ 4 = 18

Total number of buttons collected by Michael, Luke and Robert
= 1 u + 7 + 1 u + 1 u - 2
= 3 u + 5
= 3 x 18 + 5
= 59

Average number of buttons collected by Michael, Luke and Robert
= 59 ÷ 3
≈ 20 (Round off to the nearest whole number.)

Answer(s): 20