There are n-A.M is between 7 and 85 such that (n-3) th mean : n th mean isas11:24 then ‘n’ is
7,A1,A2,…An,85 are in A.P
85=n+2)th term =a+(n+1)d(n+1)d=78d=78n+1
Given that (n−3)thA⋅MnthA⋅M=1124⇒7+(n−3)d7+(n+1−1)d=1124⇒168+24(n−3)d=77+11nd ⇒91=d11n-24n+72⇒91n+1=7872-13n⇒1105n=5525⇒n=5