Question

Sum of 20 terms of 3+5+7+9+..
.is

Answer 1

S20 = 20/2×[2×1+19×2]

= 10(2+38)

= 10×40 = 400

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..

Answer 2

✪ $\huge{\red{\underline{\overline{\mathbf{Question}}}}}$ ✪

→Sum of 20 terms of 3+5+7+9... is

✪ $\huge{\green{\underline{\overline{\mathbf{Answer}}}}}$ ✪

⇒Given:

• n=20
• a=3
• Common Difference= 5-3 = 2

⇒To Find:

• Sum of 20 terms

Using formula-

⇒$\large{S_{20}=\frac{20}{2}(2\times 3+(20-1)\times 2)}$

⇒$S_{20}=10(6+(19\times 2))$

⇒$S_{20}=10\times 44$

⇒$\huge{\pink{\overbrace{\underbrace{S_{20}=440}}}}$

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Formulas Used :-

• $\large{S_{n}=\frac{n}{2}(2a+(n-1)d)}$

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