Problem 2 · 2023 Math Kangaroo
Easy
Logic & Word Problems
careful-counting
Matchsticks are arranged to form digits, as shown. For example, the number 15 needs 7 matchsticks, and so does the number 8. What is the biggest number you can build using exactly 7 matchsticks?
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Answer: D — 711
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Hint 1 of 2
Count the matchsticks each digit uses from the picture, then add up the sticks in each answer.
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Hint 2 of 2
Keep only the answers that use exactly 7 matchsticks, then take the largest of those.
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Approach: count sticks per digit, keep the total of 7, choose the biggest
- From the picture, the digit 7 uses 3 sticks and the digit 1 uses 2 sticks.
- So 711 uses 3 + 2 + 2 = 7 sticks; 31, 51 and 74 also each use 7 sticks, but 800 needs far more.
- Among the numbers built from exactly 7 matchsticks, the largest is 711.
- The answer is D.
Mark:
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