Problem 11 · 2017 Math Kangaroo
Medium
Arithmetic & Operations
careful-counting
Balloons are sold in packages of 5, 10 or 25 pieces each. Marius buys exactly 70 balloons. What is the minimum number of packages he has to buy?
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Answer: B — 4
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Hint 1 of 2
Use the biggest packages first to cut down the number of packages.
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Hint 2 of 2
Try two 25-packs, then fill the remaining 20 with the fewest packs.
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Approach: use the largest packages first
- Two packs of 25 give 50, leaving 20 balloons to reach 70.
- Make 20 with two packs of 10.
- That is 2 + 2 = 4 packages, and three packages cannot total exactly 70.
- So the minimum is 4.
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