A) 40
B) 60
C) 50
D) 72
E) 48
Correct Answer: C
Solution :
Speed\[\propto \frac{\text{1}}{\text{Time}}\] Ratio of speed \[=25:30\] \[\Rightarrow \]\[5:6\] Ratio of time \[\therefore \]1 unit = 20 minutes Time required by the first person to cover the distance of 6 units \[=20\times 6=120\]minutes = 2 hours. \[\therefore \]Total distance \[\text{=Speed }\!\!\times\!\!\text{ Time}\] \[\text{=25 }\!\!\times\!\!\text{ 2=50}\,\,\text{km}\] Method II. Let distance\[=x\,\,km\] Then, \[\frac{x}{25}-\frac{x}{30}=\frac{20}{60}\] \[\Rightarrow \] \[\frac{x(30-25)}{25\times 30}=\frac{20}{60}\] \[\Rightarrow \] \[x=\frac{25\times 30}{30-25}\times \frac{20}{60}\] ? (*) Note: For future, we can remember the step (*) as direct formula for such question. Dist.\[\text{=}\frac{\text{Product}\,\,\text{of}\,\,\text{speeds}}{\text{Diff}\,\,\text{of}\,\,\text{speeds}}\text{ }\!\!\times\!\!\text{ Diff}\,\,\text{in}\,\,\text{time}\]You need to login to perform this action.
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