Question

if the speed of a car is increased by 10 km/h it takes 18 minutes less to cover a distance of 36 km .find the speed of the car

Answer 1

Let the speed of the car be x

time taken to cover 36 km = 36/x hr

ATQ

36/x - 36/(x+10) = 18/60

(36(x+10) - 36x)/x(x+10) = 3/10

(36x + 360 - 36x)/(x^2+ 10x) = 3/10

360x10 = 3(x^2 + 10x)

3x^2 + 30x = 3600

3x^2 + 30x - 3600= 0

x^2 + 10x - 1200=0

x^2 + 40x - 30x - 1200=0

x(x+40) - 30(x+ 40)= 0

(x-30)(x+40)=0

we get 2 answers

But x=30 is the correct one

therefore the speed of the car is 30 km/hr