Question

1. By increasing the speed of a car by 10 km per hour, the time of
journey for a distance of 72 km is reduced by 36 minutes. Find the
original speed of the car. [30km/hr]​

Answer 1

Answer:

original speed is equal to 30 km/hr

Explanation:

Let original speed be x km/hr.

∴ Time = 72/x hr

New speed = x + 10 km/hr.

∴ New time = 72/x + 10 hr

Difference in time = 36 mins

∴ 72/x - 72/x + 10 = 36/60

72x + 720 – 72x/x(x + 10) = 3/5

5 × 720 = 3(x2 + 10x)

1200 = x2 + 10x

x2 + 10x – 1200 = 0

x2 + 40x – 30x – 1200 = 0

x(x + 40) – 30(x + 40) = 0

(x – 30)(x + 40) = 0

∴ x = 30