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Q.

A fire in a building B is reported on the telephone to two fire stations P and Q, 20 km apart from each other on a straight road. P observes that the fire is at an angle of 60 °   to the road and Q observes that it is at an angle of 45 °   to the road. Which station should send its team and how much will this team have to travel?

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a

7.36 km

b

6.32 km 

c

7.32 km

d

8.32 km

answer is B.

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Detailed Solution

Given that a fire in a building B is reported on the telephone to two fire stations P and Q, 20 km apart from each other on a straight road. P observes that the fire is at an angle of 60 °   to the road and Q observes that it is at an angle of 45 °   to the road.
We have to find the distance between the station and the building.
The value for the trigonometric identities can be evaluated by using the right-angled triangle the value for  can be expressed as tanθ=  opposite   adjacent   
Suppose P and Q   be two fire station 20 Km apart and point B  be the building and point A  be the fire .Assume AB=h  is the height of the building and PB=x  is the distance of the fire station P from the building. Then, by using the figure geometry,
Question Image In triangle APB tanθ = AB PB tan 60 ° = h x 3 = h x h =x 3  .............(1)    Similarly, in triangle ABO tan 45 ° = AB BQ 1 = h 20x h =20x .......... (2)   Thus, from equation (1) and (2),
x 3 =20x x( 3 +1) =20 x = 20 ( 3 +1) ( 3 1) ( 3 1) x =7.32 km    The other distance of fire station from the building is,
QB =20x QB =207.32 QB =12.68 km  Since,  PB<QB      Therefore, the station P   should send it team to travel 7.32 km.
Therefore, the correct option is 2.
 
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