Richard spent 2/7 of his money on 4 bags and 4 pencil cases. The cost of a bag
is twice that of a pencil case. With 5/6 of his remaining money, he bought more
pencil cases. How many pencil cases did he buy in all?
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Cost of 4 pencil cases = 1/3(2/7) = 2/21 or 4/42
Cost of "more pencil cases" = 5/6(5/7) = 25/42
Proportion: (4/42) / 4 = (25/42) / x x = 25
Richard bought 29 pencil cases.