A while walking towards a tower at a constant speed, 
observed that the angle of elevation of the top of the 
tower changed to 600 from 450. How much more than 
will he take to reach of the tower? 
(a) 5 min 
(c) 5 3 - 1 min 
(b) 5 3 min 
(d) None of these 

Dear Student,

Let AB be the tower, C=45° and D=60°Now, In ABC,tan 45°=ABBC1=ABBCAB=BCIn ABD,tan 60°=ABBD3=ABBDAB=3BDThus we get,BC=3BDBD+DC=3BDDC=3BD-BDDC=3-1BDSince the person walks at constant speed s, let t be time taken by him to cover CD.Thus, CD=stAlso let t' be time taken by him to cover BD.Thus, BD=st'Since, DC=3-1BDst=3-1st't=3-1t't'=t3-1=t3+13-13+1=t3+12If t=5 minutes, then required time t'=53+12 min.Hence d is correct answer.


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