A train covers a distance in 35 minutes . If the speed of the train is reduced by 10 km/hr, then the same distance is covered in 42 minutes . The distance is :

35 km

Distance = Speed × Time 

Initial time taken = 35 minutes  =  \(\frac{35}{60}\) hr 

Let distance = d km 

Speed = \(\frac{D \; ×\; 60}{35}\) =  \(\frac{12D}{7}\)

The speed of train reduced by 10 km/hr 

New speed = \(\frac{12D}{7}\) - 10 = \(\frac{12D\;-\;70 }{7}\)

New time = 42 minutes 

Distance ( D ) =  \(\frac{12D\;-\;70 }{7}\) × \(\frac{42}{60}\)

2D = 70 km

D = 35 km