The ratio of sums of n-terms of two arithematic progressions is (3n-13):(5n+21). The ratio of 24th term of the two series is?

Asked by Manan Kinjawadekar | 15th Apr, 2013, 07:14: PM

Expert Answer:

let first term and common difference of first AP be A & D and for the second AP be "a" & "d"
 
therefor (3n-13)/(5n+21)=(n/2(2A+(n-1)D))/(n/2(2a+(n-1)d))
 
therefor (3n-13):(5n+21)=(2A+(n-1)D))/(2a+(n-1)d)
 
now putting n=47 on both sides
 
(3*47-13)/(5*47+21)=(A+23D)/(a+23d)
 
therfor ratio of there 24 th term=1/2

Answered by  | 15th Apr, 2013, 08:08: PM

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