Mathematics — CBSE Class 10 board question

(C) 37

Here, $a = 3$, $d = 3$, $a_n = 111$. Using $a_n = a + (n-1)d$: $111 = 3 + (n-1)3 \Rightarrow 108 = 3(n-1) \Rightarrow n = 37$.

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 $a_{37} = 3 + 36 \times 3 = 111$ ✓.