CombinatoricsDifficulty 3.1AMC 10/12Find the answer
Six bags of marbles contain 18,19,21,23,25 and 34 marbles, respectively. One bag contains chipped marbles only. The other 5 bags contain no chipped marbles. Jane takes three of the bags and George takes two of the others. Only the bag of chipped marbles remains. If Jane gets twice as many marbles as George, how many chipped marbles are there?
Pick one
Solution
Let the number of marbles George has be x, and so the number of marbles Jane has is 2x. Therefore, the total number of non-chipped marbles is 3x≡0(mod 3). However, the total number of marbles is 18+19+21+23+25+34=140≡2(mod 3). Therefore, we need a number of chipped marbles ≡2(mod 3) to get a number of non-chipped marbles ≡0(mod 3). 18≡0(mod 3) 19≡1(mod 3) 21≡0(mod 3) 23≡2(mod 3) 25≡1(mod 3) 34≡1(mod 3) Since 23 is the only one ≡2(mod 3), it is the only possible number of chipped marbles, D. To check, we can see that if Jane takes the 19,25, and 34 marble bags and George takes the 18 and 21 marble bags, this satisfies the conditions.
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