Question

Distance between two station is 200 km. The train travel 100 km @ 50 km/h. How fast the train travel so that the average speed becomes 70 km/h.
Its very urgent please tell the answer.​

Answer 1

GIVEN

Distance between two station is 200 km.

It covers 100km with 50kmph.

Average speed = 70kmph

TO FIND Speed it covers in next 100km

SOLUTION

Average speed =

$\frac{total \: distance}{total \: time}$

$70 = \frac{200}{t} \\ \\ \implies t = \frac{200}{70}= \frac{20}{7}$

Now total time is 20/7 but time taken for first 100km is ,

$\frac{distance}{speed} \\ \\ = \frac{100}{50} \\ \\ = 2hr$

Time for remaining 100km / 2nd half =

$( \frac{20}{7} - 2)hrs \\ \\ = \frac{20}{7} - 2 \\ \\ = \frac{20 - 14}{7} \\ \\ = \frac{6}{7} hr$

Speed for second half ,

$\frac{distance}{time} \\ \\ = \frac{100}{ \frac{6}{7} } \\ \\ = \frac{700}{6} = \frac{350}{3} kmph$

Ans is 116.67kmph