Q. 23

If the sum of n terms of two arithmetic progressions are in the ratio 5n + 4 : 9n + 6, find the ratio of their 18th terms.

Answer :

For first A.P. :

Let first term = a1

Common difference = d1

and Sn1 = Sum of n terms

For second A.P. :

Let first term = a2

Common difference = d2

and Sn2 = Sum of n terms

Given =

Required to find


We have =

or =

or =

Taking = 17 or n = 34 + 1 = 35, we have = =

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