A) 12.5km/hr
B) 12km/hr
C) 13 km/hr
D) 13.5km/hr
Correct Answer: B
Solution :
Let t hr be the time taken by the man to reach his office at the speed of 15 km/h. Then, time taken to reach office at the speed of 10 km/h = (t + 2)h Now, \[{{s}_{1}}\times {{t}_{1}}={{s}_{2}}\times {{t}_{2}}\] \[\Rightarrow \]\[10 \times \left( t+ 2 \right) = 15\times t\] \[\Rightarrow \]10 t+ 20 = 15 t \[\Rightarrow \] 5t- 20 \[\Rightarrow \] t - 4 hr Now, distance covered by man to reach office = \[{{s}_{1}}\times {{t}_{1}}\Rightarrow 10\times (4+2)\] 10 x 6 = 60 km Now, speed required to reach office at Distance 12 noon i.e., in 5h = \[\frac{Dis\tan ce}{Time}\] \[\therefore \] speed = \[\frac{60}{5}\]= 12 km/h
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