Problem 12 · 2025 Math Kangaroo
Medium
Logic & Word Problems
work-backward
In the morning, the five friends Anna, Bob, Cristina, David and Eduard each have a fully charged phone battery. By evening, Bob has used up as much of his battery as Anna and Cristina together, and Bob's battery is now empty. David has not used his phone at all. The pictures show the battery levels of the five children. Which one is Eduard's battery level?
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Answer: B
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Hint 1 of 2
David did not use his phone, so his battery is still full - that pins down 'full'.
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Hint 2 of 2
Bob's used-up amount equals Anna's plus Cristina's; match the five pictures to the five children to find the leftover one for Eduard.
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Approach: assign the five battery pictures by the given clues
- David's phone is full (unused) and Bob's is empty (fully used).
- Bob's drained amount equals Anna's drain plus Cristina's drain combined.
- Match those clues to four of the five pictures; the one left over is Eduard's.
- Eduard's battery level is option B.
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