Samantha, Harper, Elizabeth and Noah share the same hobby of collecting marbles. The average number of marbles collected by the 4 friends is 28. Harper collected 7 more marbles than Elizabeth but 12 fewer marbles than Samantha. Noah collected 2 marbles fewer than Elizabeth. Find the average number of marbles collected by Harper and Noah. Round off your answer to the nearest whole number.
Number of marbles Elizabeth collected = 1 u
Number of marbles Harper collected = 1 u + 7
Number of marbles Samantha collected = 1 u + 7 + 12 = 1 u + 19
Number of marbles Noah collected = 1 u - 2

Total number of marbles collected
= 4 x 28
= 112

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

4 u + 24 = 112
4 u = 112 - 24 = 88

1 u = 88 ÷ 4 = 22

Total number of marbles collected by Harper and Noah
= 1 u + 7 + 1 u - 2
= 2 u + 5
= 2 x 22 + 5
= 49

Average number of marbles collected by Harper and Noah
= 49 ÷ 2
≈ 25 (Round off to the nearest whole number.)

Answer(s): 25