Arithmetic Progressions
NCERT Exemplar
CBSE
Grade 10
Question:
If the $11^{\text{th}}$ term of an AP is $-61$ and its first term is $4$, then its common difference is:
(a) $-6.5$
(b) $-6.1$
(c) $-6.7$
(d) $-6.2$
Step-by-Step Solution
Key Concept: $a_{11} = a + 10d$.
$a_{11} = 4 + 10d = -61 \Rightarrow 10d = -65$. [0.5 Mark]
$d = -6.5$. [0.5 Mark]
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🎯 Official CBSE Marking Scheme:
Formula substitution $a_{11} = a + 10d$: 0.5 Mark
Solving for $d = -6.5$: 0.5 Mark
Correct Answer: $-6.5$
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