A train covers a distance of 90 km at a uniform speed. Had the speed been 15 km / hour more, it would have taken 30 minutes less for the journey. Find the original speed of the train.
Time = distance/speed
Given, train covers a distance of 90 km at a uniform speed. Had the speed been 15 km / hour more, it would have taken 30 minutes less for the journey.
Let the usual speed be ‘a’.
⇒ 90 ×(a + 15 –a) = (a2 + 15a)/2
⇒ a2 + 15a – 2700 = 0
⇒ a2 + 60a – 45a – 2700 = 0
⇒ a(a + 60) – 45(a + 60) = 0
⇒ (a + 60)(a – 45) = 0
⇒ a = 45 km/hr