Question

The sum of n terms of two ap are in the ratio 5n+4:9n+6. Find the ratio of there 18th term

Answer 1

Let a and d be the first term and common difference of the 1st AP Then, a1=S1=5*1+4=9 S2=5*2+4=14 a2=14-9=5 a18=9+17*(14-9)=-76 Let A and D be the first term and common difference of the 2nd A.P. Similarly, A1=15 A2=-6 A18 =-87 Reqd. Ratio= 76:87

Answer 2

44:177 is the answer I think