Problem 20 · 2018 Math Kangaroo
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Logic & Word Problems
casework
The five balls weigh 30 g, 50 g, 50 g, 50 g and 80 g. The three balances show how groups of the balls compare. Which of the balls weighs 30 g?
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Answer: C — C
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Hint 1 of 2
Read each balance: the lower pan holds the heavier total.
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Hint 2 of 2
Combine the comparisons to order the balls; the lightest single ball is the 30 g one.
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Approach: deduce the order of weights from the balances
- The weights are 30, 50, 50, 50, 80 g, so one ball is uniquely the lightest (30 g).
- Each balance tells which pair is heavier, and chaining these comparisons orders the balls.
- The ball that comes out lightest is C, so C weighs 30 g.
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