Answers

2014-08-10T16:51:04+05:30
Let velocity of A is a, and velocity of B is b.

Time taken by A to cover 30 kms. = \frac{30}{a}

Time taken by B to cover 30 kms. = \frac{30}{b}

After doubling the velocity, time taken by A = \frac{30}{2*a}

Now we have two equations
\frac{30}{a} =  \frac{30}{b} + 3 \\  \\  \frac{30}{2a}  =  \frac{30}{b} -  \frac{3}{2}

Solving equations gives, a =  \frac{10}{3} km/hr \\  \\ b = 6km/hr
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2014-08-10T17:30:48+05:30
30/v1-30/v2 =3
30/2v1 -30/v2 = -1.5
subtracting the two equations
30/2v1 = 4.5
v1 = 15/4.5 = 30/9 = 10/3 =3.333 km/hr
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