Question

A train travels at a certain average speed for a distance of 63 km and then travels a distance of 72 km at an average speed of 6 km/h more than its original speed. If it takes 3 hours to complete the total journey, what is its original average speed?

Answer 1

Solution : Let its original average speed be x km/h. Therefore,

i.e., 21 (x + 6) + 24x = x (x + 6)

i.e., 21x + 126 + 24x = x2 + 6x

i.e., x2 – 39x – 126 = 0

i.e., (x + 3) (x – 42) = 0

i.e., x = – 3 or x = 42

Since x is the average speed of the train, x cannot be negative.

Therefore, x = 42.