A train covers the first $5 k m$ of its journey at a speed of $30 k m / h r$ and the next $15 k m$ at a speed of $45 k m / h r$ . What is the average speed of the train?

35 k m / h r

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37.5 k m / h r

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39.5 k m / h r

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40 k m / h r

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Solution

The correct option is D $40 k m / h r$
$T o t a l D i s t a n c e = 5 + 15 = 20 K m$

and $T o t a l T i m e = \frac{5}{30} + \frac{15}{45} \Rightarrow \frac{1}{2} H r$

Average Speed $= \frac{T o t a l D i s t a n c e}{T o t a l T i m e} = \frac{20}{\frac{1}{2}} = 40 k m / h r$

Therefore, Answer is $D$

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