<PRE><B>Question 840890</B>
Let he original speed be x and differenc in time is 1/4. then increase in speed by 2 will be x+2

time taken = distance / speed
original time taken = 15/x 
time taken after increase in speed by 2 km/hr to cover the same distance = 15/x+2

difference in time = 1/4
15/x-15/(x+2)=1/4
(15(x+2) - 15x)/x(X+2) = 1/4
4(15(x+2-x)=x^2+2x
120 = x^2 +2x
x^2+2X -120 = 0
factorizing above equation we get 
(x+12)(x-10)=0
X=-12 X=10
Negotiating negative we have x = 10

Therefore the original speed is 10 km/hr </PRE>