NCERT · Class 10 · Mathematics · Arithmetic ProgressionsWhat is the 20th term from the last term (towards the first term) of the AP: 3, 8, 13, ..., 253?
Step-by-Step Solution
To find the $n$-th term from the end, we can reverse the AP or use the formula: $a_n$ from end = $l - (n - 1)d$, where $l = 253$, $d = 5$, and $n = 20$. Thus, $253 - (20 - 1)5 = 253 - 19(5) = 253 - 95 = 158$. Therefore, the correct option is B.
Detailed Options Breakdown
Option : 153
Incorrect choice. This distractor represents a common misunderstanding of the core principles of Arithmetic Progressions.
Option 1: 158 (Correct Answer)
Correct choice. Refer to the step-by-step verified solution guidelines above for details.
Option 2: 163
Incorrect choice. This distractor represents a common misunderstanding of the core principles of Arithmetic Progressions.
Option 3: 168
Incorrect choice. This distractor represents a common misunderstanding of the core principles of Arithmetic Progressions.
💡 Study Guide: This question tests core syllabus concepts from Arithmetic Progressions. For formulas, key summaries, and mock exam reference guides, read the full Arithmetic Progressions Revision Notes.