Bunuel wrote:
Two men A and B walk from P to Q a distance of 21 km at rates 3 and 4 km an hour respectively. B reaches Q and returns immediately and meets A at R. The distance from P to R is:
A. 14 km
B. 16 km
C. 18 km
D. 20 km
E. 22 km
We can let t = the time, in hours, it takes B to meet A at R. We also must recognize that when they meet at R, together they have walked exactly twice the distance of 21 km (of course, B walks more than 21 km and A walks less than that). Therefore, we can create the equation:
3t + 4t = 2(21)
7t = 42
t = 6
Therefore, A and B both have walked 6 hours when they meet at R. Therefore, the distance from P to R is also the distance walked by A, which is 6 x 3 = 18 km.
Answer: C
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