Determine the number of terms in the terms in the A.P. 3,7,11…407. Also, find its 20th term from the end.

Explanation

Here, first term `a=3` and common difference `d=4`.

Let there be n terms in the given A.P. Then,

`n ^(th)`term `=407`

`⇒407=3+(n−1)×4`

`⇒n=102`

So, there are 102 terms in the given A.P.

Now, `20 ^(th)`
term from the end
...