Problem 21 · 2017 Math Kangaroo
Stretch
Arithmetic & Operations
groupingtotal-then-divide
Five boys share 10 bags of marbles between themselves. Everyone gets exactly two bags (see picture). Alex gets 5 marbles, Bob 7, Charles 9 and Dennis 15. Eric gets the two bags that are left over. How many marbles does he get?
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Answer: E — 19
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Hint 1 of 2
The ten bags hold 1, 2, 3, ... up to 10 marbles; add them all first.
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Hint 2 of 2
Subtract the four known boys' totals from the grand total to get Eric's two bags.
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Approach: total all bags, then subtract the known amounts
- The ten bags hold 1 through 10 marbles, a total of 55.
- Alex, Bob, Charlie and Dennis took 5 + 7 + 9 + 15 = 36 marbles.
- Eric gets the two leftover bags: 55 - 36 = 19.
- So Eric gets 19 marbles.
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