Q1. [1] § 5.2 Arithmetic Progressions § 5.5 Summary
The number of terms in the A.P. 3, 6, 9, 12, …, 111 is :
- A $36$
- B $40$
- C $37$
- D $30$
Previously asked in CBSE board exam
2024 30/5/1 Q11
Generated by claude-sonnet-4-6 · 2026-06-15 10:31 · grounding rag
Model Answer
(C) 37
Here, $a = 3$, $d = 3$, $a_n = 111$. Using $a_n = a + (n-1)d$: $111 = 3 + (n-1)3 \Rightarrow 108 = 3(n-1) \Rightarrow n = 37$.
Explanation
Use the formula $a_n = a + (n-1)d$ with the last term as $a_n$. Solve for $n$. A common mistake is forgetting to add 1 after dividing — always verify by checking $a_{37} = 3 + 36 \times 3 = 111$ ✓.
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