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2014 Math Kangaroo

Problem 11

Problem 11 · 2014 Math Kangaroo Medium
Logic & Word Problems careful-counting

In a holiday camp, 7 children eat ice cream every day and 9 children eat ice cream every other day. The rest never eat ice cream. Yesterday 13 children ate ice cream. How many children will eat ice cream today?

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Answer: D — 10
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Hint 1 of 2
The 7 daily eaters had ice cream yesterday and will have it again today.
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Hint 2 of 2
Figure out how many of the every-other-day group ate yesterday; the rest of that group are the ones who eat today.
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Approach: split the 13 into daily eaters and every-other-day eaters
  1. The 7 daily children ate yesterday, so 13 − 7 = 6 of the every-other-day children also ate yesterday.
  2. Those 6 skip today, so the other 9 − 6 = 3 every-other-day children eat today.
  3. Today's total is the 7 daily children plus those 3, which is 10.
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