A motorboat traveling at a speed of $20 k m$ in one hour is used to transport fish. If it starts from the dockyard towards a point in the sea at a distance of $40 k m$ to collect $10 k g$ of fish and return back to the dockyard to empty the boat. How much time will it take for the motorboat to transport $30 k g$ of fish?

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$6 h o u r s$

$8 h o u r s$

$10 h o u r s$

$12 h o u r s$

answer is D.

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Detailed Solution

The correct option is (D),
Given the speed of the motorboat = $20 k m$ in one hour
The boat will travel a distance of $20 k m$ in one hour
The point in the sea where the fish is to be collected from is $40 k m s$ away.
Time taken by the boat to reach that point is given by dividing the total distance by the speed of the motorboat i.e.
$= \frac{40}{20} = 2$

Hence, the time taken by the boat to reach the point in the sea is $2$ hours.
It will collect $10 k g s$ of fish from there and return to the dockyard. This distance is the same as $40 k m$ . Hence it will take $2$ more hours to return with $10 k g$ of fish.
The total time taken to transport $10 k g$ of fish is $4 h o u r s$ .
The time taken to transport $30 k g$ will be $3$ such trips.
Hence, $4 \times 3 = 12$
Therefore, the time taken by the boat to transport $30 k g$ of fish will be $12$ hours.