QA – Placement Quizzes | Time Speed Distance | Question 10

A train covers a journey of 4 stations connected to form a square at speeds of 20, 40, 60 and 80 km/hr. What is the average speed of train for this journey?
(A) 38.4
(B) 100
(C) 80.4
(D) 160


Answer: (A)

Explanation: Speed = distance/time

Say, side of square = y km

time t1 = y/20



t2 = y/40, t3 = y/60 and t4 = y/80

Total time = (12+6+4+3)y/240

speed = total distance/total time

= 4y/(t1+t2+t3+t4) = 4y*240/25y = 38.4 km/hr

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