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1)

If a,b,c be positive integers such that b/a is an integer. If a,b,c are  in geometric  progression and the arithmetic mean of a,b,c is b+2, then the value of   ab+a14a+1  is 


A) 5

B) 4

C) 3

D) 2

Answer:

Option B

Explanation:

Plan 

(i)  a,b,c are in G.P ,

 then they can be taken as a, ar, ar2 where r,(r ≠ 0)  is the common ratio

 (ii) Arithmetic mean of x1,x2,............xn

= x1+x2+....+xnn

  Let a,b,c are a,ar, ar2  , where rε N

Also,    a+b+c3=b+2

              a+ar+ar2= 3(ar)+6

           ar2-2ar+a =6

                    (r-1)26a

              6/a must be perfect square   a ε N

     a can be 6 only.

           r1=±1r=2

 and            ab+a14a+1=36+6147=4