A train when moves at an average speed of 40 kmph, reaches its destination on time. When its average speed becomes 35 kmph, then it reaches its destination 15 minutes late. Find the length of journey.
Select:
A) 70 km B) 80 km C) 40 km D) 20 km E) None
Sol.   Difference between timings = 15 min = 1/4 hr.   Let the length of journey be x km.   Then, x/35 - x/40 = 1/4   ⇔ 8x - 7x = 70   ⇔ x = 70 km.   70 kmnswer 70 km
<result>A</result>
A train when moves at an average speed of 40 kmph, reaches its destination on time. When its average speed becomes 35 kmph, then it reaches its destination 15 minutes late. Find the length of journey.