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A boy spends ₹ 10 on first day, ₹ 20 on second day, ₹ 40 on third day and so on. Find how much in all, will he spend in 12 days?

GP

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Answer

G.P. formed = 10 + 20 + 40 + ……..

Common ratio (r) = 2010\dfrac{20}{10} = 2.

⇒S=a(rn−1)(r−1)..........(As∣r∣>1)=10(212−1)2−1=10(212−1).\Rightarrow S = \dfrac{a(r^n - 1)}{(r - 1)} ……….(As |r| \gt 1)\\[1em] = \dfrac{10(2^{12} - 1)}{2 - 1} \\[1em] = 10(2^{12} - 1).

Hence, ₹10(212 - 1).

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