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SEQUENCES AND SERIES — MATHS STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceMATHSSEQUENCES AND SERIES1 Mark
MCQ
If in an A.P., first term is 20 and 12th term is 120. Find the sum up to 12th term.
  • A
    420
  • ✓
    840
  • C
    140
  • D
    680
✓

Answer

Correct option: B.
840
  1. 840
Solution:
Given, $a = 20, a_{12}= 120, n = 12$
$\text{s}_{\text{n}}=\frac{\text{n}}{2}(\text{a}+\text{I})$
$\Rightarrow\text{s}_{\text{12}}=\frac{12}{2}(20+120)$
$= 6 \times 140 = 840$

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