Question:medium

Find the \(20^{th}\) term from the last term of the AP : 3, 8, 13, …..., 253

Updated On: Jan 13, 2026
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Solution and Explanation

The given arithmetic progression (A.P.) is \(3, 8, 13, …, 253\).
The common difference for this A.P. is \(5\).
When this A.P. is written in reverse order, it becomes:
\(253, 248, 243, ….., 13, 8, 5\)
For this reversed A.P.:
\(a = 253\)
\(d = 248 − 253 = −5\)
\(n = 20\)
The 20th term, \(a_{20}\), is calculated as: \(a_{20 }= a + (20 − 1) d\)
Substituting the values: \(a_{20 }= 253 + (19) (−5)\)
Further calculation: \(a_{20} = 253 − 95\)
\(a_{20} = 158\)

Thus, the \(20^{th}\) term from the last term of the original A.P. is \(158\).

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