Question

A car covers a distance of 400 km at a certain speed. Had the speed been 40 km/h more,
the time taken for the journey would have been 30 minutes less. Find the original speed of the
car.

Answer 1

Answer:

48km/h

Step-by-step explanation:

0

votes

answered Feb 15, 2019 by navnit40 (-4,938 points)

Let the original speed of the car be x km/hr

so, Time taken by car = 400/x hrs

Again, speed = (x + 12) km/hr

Time taken by car = 400/x + 12

So, 400/x – 400/x + 12 = 1 hr + 40/ 60

400. (x + 12 – x)/x(x + 12) = 5/3

4800/x2 + 12x = 5/3

⇒ 5(x2 + 12x) = 14400

⇒ x2 + 12x – 2880 = 0

⇒ x2 + 60x – 48x – 2880 = 0

⇒ x(x + 60) – 48(x + 60) = 0

⇒ (x + 60)(x – 48) = 0

Either, x + 60 = 0

x = - 60

(Neglect, speed can’t be negative)

or x – 48 = 0

x = 48

⇒ Original speed of the car is 48 km/hr.

Answer 2

hope it's helpful to you