A jeep covers a distance of 180 km at a certain speed. If the speed is increased by 15 km/h, it takes 1 hour less.
Find the original speed.
Show answer & explanation
Correct answer: A
Explanation
Distance = 180 km
Difference in time = 1 hour
Let the original speed be = x
Time = 180/x
New speed = x + 15
New time = 180/(x + 15)
180/x − 180/(x + 15) = 1
[180(x + 15) − 180x] / [x(x + 15)] = 1
180x + 2700 − 180x = x(x + 15)
2700 = x² + 15x
x² + 15x − 2700 = 0
(x + 60)(x − 45) = 0
x = 45 km/h