A journey of 180 km takes 6 hours more when the speed of a bike is reduced by 8 km/h. What is the original speed of the bike?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 20 km/h.
Let original speed = x km/h
180/(x − 8) - 180/x = 6
⇒ 30/(x − 8) - 30/x = 1
⇒ 240 = x(x − 8)
⇒ x2 - 8x - 240 = 0
⇒ (x - 20)(x + 12) = 0
⇒ x = 20 km/h