Sofia, Harper, Julian and Isaac share the same hobby of collecting buttons. The average number of buttons collected by the 4 friends is 27. Harper collected 9 more buttons than Julian but 12 fewer buttons than Sofia. Isaac collected 2 buttons fewer than Julian. Find the average number of buttons collected by Harper and Isaac. Round off your answer to the nearest whole number.
Number of buttons Julian collected = 1 u
Number of buttons Harper collected = 1 u + 9
Number of buttons Sofia collected = 1 u + 9 + 12 = 1 u + 21
Number of buttons Isaac collected = 1 u - 2

Total number of buttons collected
= 4 x 27
= 108

Total number of buttons collected in units
= 1 u + 1 u + 9 + 1 u + 21 + 1 u - 2
= 4 u + 28

4 u + 28 = 108
4 u = 108 - 28 = 80

1 u = 80 ÷ 4 = 20

Total number of buttons collected by Harper and Isaac
= 1 u + 9 + 1 u - 2
= 2 u + 7
= 2 x 20 + 7
= 47

Average number of buttons collected by Harper and Isaac
= 47 ÷ 2
≈ 24 (Round off to the nearest whole number.)

Answer(s): 24