Liam, Jacob, Evan and Risa share the same hobby of collecting buttons. The average number of buttons collected by the 4 friends is 23. Jacob collected 9 more buttons than Evan but 12 fewer buttons than Liam. Risa collected 2 buttons fewer than Evan. Find the average number of buttons collected by Jacob and Risa. Round off your answer to the nearest whole number.
Number of buttons Evan collected = 1 u
Number of buttons Jacob collected = 1 u + 9
Number of buttons Liam collected = 1 u + 9 + 12 = 1 u + 21
Number of buttons Risa collected = 1 u - 2

Total number of buttons collected
= 4 x 23
= 92

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

4 u + 28 = 92
4 u = 92 - 28 = 64

1 u = 64 ÷ 4 = 16

Total number of buttons collected by Jacob and Risa
= 1 u + 9 + 1 u - 2
= 2 u + 7
= 2 x 16 + 7
= 39

Average number of buttons collected by Jacob and Risa
= 39 ÷ 2
≈ 20 (Round off to the nearest whole number.)

Answer(s): 20