Question

a train takes 2 hours less for a journey of 300 km if its speed is increased by 5 km per hour from

Answer 1

let speed be x and time taken be t

300/x=t. .......(1)

300/(x+5)=t-2........….(2)

subtract (2) from (1)

300/x-300/(x+5)=2

take 300 common

300{1/x-1/(x+5)}=2

1/x-1/(x+5)=1/150

x+5-x/x(x+5)=1/150

5/x(x+5)=1/150

1/x(x+5)=1/750

x(x+5)=750

x^2 +5x -750=0

(x+30)(x-25)=0

either x=25 or x=-30

since speed cannot be negative

therefore x=25