Question

If the ratio of the sum of the first 10 terms of 2 ap is 7 and + 1 ratio 4 and + 27 then find the ratio of their 9th terms

Answer 1

First of all, write the sum of both the APs.

7n+1 = n/2(2a1 + (n-1)d1)

4n+27 = n/2(2a2 + (n-1)d2)

Given,

7n+1:4n+27 = 2a1 + (n-1)d1:2a2 + (n-1)d2

By substituting n as 17, we will get the 9th term of each of the APs, i.e, a+8d.

There fore the ratio of their 9th terms will be 120:95 or 24:19.


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