Probus wrote:
A man travels from City A to City B at 60 miles/hr, and returns to city A at 40 miles/hr. If the entire journey took 10 hrs in all then what is the distance between City A and City B?
(A)120
(B)240
(C)272
(D)280
(E)288
The trap answer is A. Total time represents time for the round trip = 2D. No need to divide by 2.
At one rate, HALF the round-trip distance took = \(\frac{D}{60}\) hours
And at another rate, the other HALF of the trip took \(\frac{D}{40}\) hours.
Total distance in the sum of hours = 2D
Time from A to B: \(\frac{D}{r}=\frac{D}{60}\)
Time from B to A \(=\frac{D}{40}\)
Those two times sum to 10 hours
\((\frac{D}{60}+\frac{D}{40})=10\)
Multiply all terms by LCM = 120
\(2D+3D=1,200\)
\(5D=1,200\)
\(D=240\)
Answer B
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