Question

A passenger train takes 3 hours less for a journey of 360 km if its speed is increased by 10 km/hr from the usual speed . what is its usual speed ?

Answer 1

Answer:

The usual speed of train is 30 km/hr.

Step-by-step explanation:

Let the usual speed be s.

$time=\frac{distance}{speed}$

It is given that train takes 3 hours less for a journey of 360 km if its speed is increased by 10 km/hr from the usual speed.

$\frac{360}{s}-\frac{360}{s+10}=3$

$\frac{360s+3600-360s}{s(s+10)}=3$

$3600=3s(s+10)$

Divide both sides by 3.

$1200=s^2+10s$

$s^2+10s-1200=0$

$s^2+40s-30s-1200=0$

$s(s+40)-30(s+40)=0$

$(s+40)(s-30)=0$

$s=-40,30$

Since speed can not be negative, therefore the usual speed of train is 30 km/hr.