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An aeroplane flying horizontally , 1km above the ground , is observed at an elevation of `60^@` ,after 10 seconds , its elevation is observed to be `30^@` . Find the speed of the aeroplane in km/hr.

A

`120sqrt3` km/hour

B

`240sqrt3` hour

C

`250sqrt3` km/hour

D

none of these

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The correct Answer is:
B
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