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Mathematics · 2022 · 2 marks
CBSE 2022 · Region 2 · Set 1 · Q6
Find the sum of first 20 terms of an A.P. whose n^th term is given as a_n =5-2 n.
Find the sum of first $\displaystyle 20$ terms of an A.P. whose $\displaystyle \mathrm{n}^{\text {th }}$ term is given as $\displaystyle \mathrm{a}_{\mathrm{n}}=5-2 \mathrm{n}$.
Marking-scheme solution
\[\begin{array}{l}
a_{1}=5-2=3 \\
a_{20}=5-40=-35 \\
S_{20}=\frac{20}{2}(3-35)=-320
\end{array}
\]SECTION-B
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CBSE Class 10 Mathematics past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.