Question

By increasing the speed of a car by 10 km/hr,
the time of journey for a distance of 72 km
is reduced by 36 min. Find the original opeed​

Answer 1

Let the speed of a car be x km/hr

Time taken to travel with x km/hr=72/x

New speed of the car=x+10 km/hr

Time taken to travel with x+10 km/hr=72/(x+10)

As per the sum

72/x-72/(x+10)=36/60

72(x+10)-[72(x)]=36/60

72x+720-72x=3/5(x^2+10x)

1200=x^2+10x

x^2+10x-1200=0

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

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

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

x-30=0,,,,,x+40=0

x=30 km/hr,,,,,,x=-40 km/hr

Speed positive so we should consider 30 km/hr

So the answer is 30km/hr