Find the 20th term from the last term of the AP 3, 8, 13, .....253.

Dear Student!

Here is the answer to your query.

To find 20^{th} term from the last of the A. P. 3, 8, 13 ... 253

we have to find 20^{th} term of the reverse A. P. i.e. 253 ... 13, 8, 3

In the new A.P. first term *a* = 253 and common difference *d* = 3 – 8 = –5

We know that

*a _{n}* =

*a*+ (

*n*– 1)

*d*

⇒ *a*_{20} = 253 + (20 – 1) (–5)

= 253 + 19 × (–5)

= 253 – 95 = 158

Hence 20^{th} term from the last of the A.P. 3, 8, 13 ... 253 is 158.

Cheers!

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