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Let Carl has $ C , David has $ D , Hilbert has $ H , thenCarl has $9 more than David does :C = D + 9
D = C - 9.....(1)Hilbert has 1/3 of the amount of Carl :H = C/3 .....(2) they have a total amount of $61 :C + D + H = 61 .....(3)Sub (1) , (2) into (3) :C + (C - 9) + C/3 = 613C + 3C - 27 + C = 1837C = 210C = 30D = 30 - 9 = 21H = 30/3 = 10Carl has $ 30 , David has $ 21 , Hilbert has $ 10.2)Let x be the number of marbles in the smaller group , then the big group has
72 - x marbles.So we have 7x = 5(72 - x)7x = 360 - 5x12x = 360x = 30The number of marbles in the smaller group is 30.

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