A person travels in a car from his village to a town at a speed of $50$ km/hr for four hours. There he spends an hour moving about $20$ kms. He then returns to his village at a speed $40$ km/hr. His average speed over the whole journey (in km/hr) is :

44

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42

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44 \frac{4}{9}

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46 \frac{2}{3}

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Solution

The correct option is C $42$
Speed of car going from village to town= $50 k m / h r$
Time taken= $4 h r$
$∴$ Total distance from village to town= $s \times t$
$= 50 k m / h r \times 4 h r$
$= 200 k m$
Distance the man moved during a hour= $20 k m$
When man moved back from town to village
Speed of car= $40 k n / h r$
Time taken= $\frac{D}{5} = \frac{20 k m}{40 k m / h r} = 5 h r$
$∴$ Average speed= $\frac{T o t a l d i s t a n c e}{T o t a l t i m e}$
$= \frac{(200 + 20 + 200) k m}{(4 + 1 + 5) h r}$
$= \frac{420}{10} k m / h r$
$= 42 k m / h r$

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