`a`, `b`, `c`, `d` are in increasing `G.P.` If the `AM` between `a` and `b` is `6` and the `AM` between `c` and `d` is `54`, then the `AM` of `a` and `b` is
A
`15`
B
`48`
C
`44`
D
`42`
Text Solution
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The correct Answer is:
D
`(d)` Let `r` is the common ratio. `implies(a+ar)/(2)=6` and `(ar^(2)+ar^(3))/(2)=54` `impliesr^(2)=9impliesr=+-3impliesr=3(r ne -3)` When `r=3`, `a=3, `AM` of `a` and `d=(a+ar^(3))/(2)=42`
