Question

A train travels a distance of 480km at a uniform speed. If the speed had been 8km/h less, then it

would have taken 3 h more to cover the same distance. Find the speed of the train.

OR

The speed of boat in still water is 15km/h. It can go 30km upstream and return downstream to

the original point in 4 hours 30 minutes. Find the speed of the stream.​

Answer 1

Answer:

Let the speed of the train be x km/hr. Then

Time taken to travel a distance of 480km=  

x

480

​  

hr

Time taken by the train to travel a distance of 480km with the speed (x−8)km/hr=  

x−8

480

​  

hr

It is given that if the speed had been8km/hr less, then the train would have taken 3 hours more to cover the same distance

∴  

x−8

480

​  

=  

x

480

​  

+3

⇒  

x−8

480

​  

−  

x

480

​  

=3⇒  

x(x−8)

480(x−x+8)

​  

=3⇒480×8 /x[x-8]=3

⇒3x(x−8)=480×8⇒x(x−8)=160×8⇒x  

2

−8x−1280=0

This is the required quadratic equation.

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