A man reaches his office 20 min late, if he walks from his home at 3 km per hour and reaches 30 min early if he walks 4 km per hour. How far is his office from his house ?	Choose the most appropriate option.
A) 50 km B) 80 km C) 20 km D) 10 km E) 30 km
Explanation:   Let distance = x km.   Time taken at 3 kmph : dist/speed = x/3 = 20 min late.   time taken at 4 kmph : x/4 = 30 min earlier   difference between time taken :   30-(-20)= 
<gadget id="calculator">  30-(-20)</gadget>
<output>50</output>
50 mins= 50/60 hours.   x/3- x/4 = 50/60   x/12 = 5/6   x = 10 km.   Answer: 10 km
<result>D</result>
A man reaches his office 20 min late, if he walks from his home at 3 km per hour and reaches 30 min early if he walks 4 km per hour. How far is his office from his house ?