Home > Arithmetic Progressions > CBSE > 0c8accef-9d20-4385-8423-832e56ab6bda
Not the exact question you were looking for?

Paste your question to our Mathbee AI Mentor below to get an instant step-by-step solution.

Arithmetic Progressions
NCERT Exemplar
CBSE
Grade 10

Question:

If the $21^{\text{st}}$ term of the AP whose first two terms are $-3$ and $4$ is:
(a) $17$
(b) $137$
(c) $143$
(d) $-143$

Step-by-Step Solution

Key Concept: Here $a = -3$, common difference $d = 4 - (-3) = 7$. $a_{21} = a + 20d$.
$a = -3, d = 7$. [0.5 Mark]
$a_{21} = -3 + 20(7) = -3 + 140 = 137$. [0.5 Mark]

---
🎯 Official CBSE Marking Scheme:
Finding common difference $d = 7$: 0.5 Mark
Calculating $a_{21} = 137$: 0.5 Mark

Correct Answer: $137$
Mathbee AI Mentor (Free Demo)

Confused by the solution? Ask the AI to explain a specific step, tell you where you went wrong, or break down the key trap in this question.

Master Arithmetic Progressions with Mathbee

Practice this topic under real exam conditions with strict timers, or ask our AI Mentor to explain the concepts step-by-step.

Start Practicing for Free