Feb 29, A Unique Day - 2

Algebra Level 4

N = x = 29 200 x 3 2 x 2 x 2 x = 2 29 x 3 2 x 2 x 2 \large N = \ \dfrac{\displaystyle \sum_{x=29}^{200} \dfrac{x^3-2x^2}{x^2}}{\displaystyle \sum_{x=2}^{29} \dfrac{x^3-2x^2}{x^2}}

Compute N \lfloor N \rfloor .


The answer is 51.

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1 solution

Akshat Sharda
Feb 28, 2016

N = x = 29 200 x 3 2 x 2 x 2 x = 2 29 x 3 2 x 2 x 2 = x = 29 200 x 2 x = 2 29 x 2 = n = 27 198 x x = 0 27 x = x = 1 198 x x = 1 26 x x = 0 27 x = 198 199 2 26 27 2 27 28 2 = 51.19 N = 51.19 = 51 \begin{aligned} N & = \frac{\displaystyle \sum_{x=29}^{200} \frac{x^3-2x^2} {x^2}}{\displaystyle \sum_{x=2}^{29} \frac{x^3-2x^2}{x^2}} = \frac{ \displaystyle \sum^{200}_{x=29}x-2 }{ \displaystyle \sum^{29}_{x=2}x-2 } \\ & = \frac{ \displaystyle \sum^{198}_{n=27}x }{ \displaystyle \sum^{27}_{x=0}x } = \frac{ \displaystyle \sum^{198}_{x=1}x-\displaystyle \sum^{26}_{x=1}x }{ \displaystyle \sum^{27}_{x=0}x } \\ & = \frac{ \frac{198\cdot 199}{2}-\frac{26\cdot 27}{2} }{\frac{27\cdot 28}{2}}=51.19 \\ \Rightarrow \lfloor N \rfloor & = \lfloor 51.19 \rfloor=\boxed{51} \end{aligned}

I did same..

Btw, how is preparation of science?

Dev Sharma - 5 years, 3 months ago

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Hey !! Science preparation is going good ! But I have to work hard for Biology !! what about you ?

Akshat Sharda - 5 years, 3 months ago

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i am also studying biology

Dev Sharma - 5 years, 3 months ago

How do you remove the -2 ???

Ραμών Αδάλια - 5 years, 3 months ago

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When I removed the -2, I subtracted 2 from the summation's limits.

See -

x = 29 200 x 2 = x = 27 198 x \displaystyle \sum^{200}_{x=29}x-2 = \displaystyle \sum^{\color{#D61F06}{198}}_{x=\color{#D61F06}{27}}x

Akshat Sharda - 5 years, 3 months ago

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