Q.

In  ΔABC,D and E are points on BC and AC respectively such that BD=2DC and AE=3EC. Let P be the point of intersection of AD and BE. The ratio BP: PE has the value 

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a

8 : 3

b

9: 4 

c

5 : 2

d

7 : 3

answer is C.

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Detailed Solution

Consider the following diagram:      
Question Image
There’s no loss of generality in assuming A to be the origin 0 , and B and C be the points b and c respectively. By the section formula,
 Db+2c3,E=3c4                                   
The equations of AD can be written (in parametric form) as:
 Question Image          
Similarly, the equation of BE can be written as
Question Image           .
AD and BE intersect at P. Thus, the position vector of P must satisfy the equations of both AD and BE. This means that we must have
Question Image                               
Question Image                         
Since b and c are non—collinear, we must have
     Question Image=0    and  Question Image=0
This system upon solving yields Question Image
Thus, the position vector of P can be obtained by substituting the value of Question Image in the equations for AD (or BE).
                         Question Image                       
We now know the position vectors of B, P and E. We simply need to find BP:PE. Suppose this is m: 1. Then,
     Question Image                    
Question Image
Thus,            BP : PE = 8 : 3
The correct option is (C).

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