a.p

Asked by  | 8th Mar, 2008, 09:22: PM

Expert Answer:

If the ratio of the sum of n terms of two AP is (4n+2): (3n+47)

we need to find the ratio of the 9th term
Let a,a' and d, d' are the first term and common difference of the two APs
general term of the AP = a+(n-1)d and = a'+(n-1)d'

Sum to n terms of the AP will be n/2(2a+(n-1)d) and n/2(2a'+(n-1)d')
(2a+(n-1)d) /(2a'+(n-1)d') = (4n+2): (3n+47) 
(a+(n-1)/2d ): (a'+(n-1)/2d') = (4n+2): (3n+47) 
Substitute n = 17 on both sides to get the ratio of 9th term
(a+8d ):(a'+8d') = 5:7

Answered by  | 10th Mar, 2008, 01:11: PM

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