Find the 7th term from the end of the A.P. : 3,8,13,18,.....,98.

Explanation

Here, l=98,
`d=8-3=13-8=5`,
`n=7`
`:. ` 7th term from the end -`l-(7-1)d`
`=98-6xx5=98-30=68`
Alternative Method :
Write the A.P. in reverse order `98,...18,13,8,3`
Hence, a=98,
`d=3-8=8-13=-5`
`:. a_(7)=a+(7-1)d`
`=98+6xx(-5)=98-30=68`
which is the 7th term from the end of the given A.P.
Trick : 7th term from the end of A.P. `3,8,13,....98` means 7th term from the beginning of A.P. 98,...,18,13,8,3.