Problem 11 · 2020 Math Kangaroo
Medium
Arithmetic & Operations
Logic & Word Problems
work-backward
As soon as he left his city heading toward Caecá, Charles saw the sign on the left. When he came back from Caecá, he saw the sign on the right. At that point, how far was it to reach his city?
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Answer: D — 41 km
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Hint 1 of 2
The left sign (just outside his city) reads Arati 12 km, Baibá 33 km; the right sign reads Baibá 8 km, Arati 29 km.
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Hint 2 of 2
First use either sign to find the fixed gap between Arati and Baibá, then notice his city sits 12 km past Arati.
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Approach: use the fixed town distances on the two signs
- He saw the left sign just as he left his city, so his city is 12 km before Arati (and Baibá is 33 km out).
- On the way back the right sign reads Arati 29 km ahead; his city is another 12 km beyond Arati.
- So the distance left to his city is 29 + 12 = 41 km.
- The answer is 41 km, choice D.
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