Just for fun!-X

Find the remainder when ( 2 + 4 + 6 + + 2014 ) (2+4+6+\ldots+2014) is divided by ( 1 + 3 + 5 + + 2013 ) (1+3+5+\ldots+2013) .


The answer is 1007.

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3 solutions

Rohit Ner
Aug 18, 2015

2 + 4 + 6 + + 2014 1 + 3 + 5 + + 2013 = 1 + 1 + 3 + 1 + 5 + 1 + + 2013 + 1 1 + 3 + 5 + + 2013 = 1 + 3 + 5 + + 2013 + 1007 1 + 3 + 5 + + 2013 \begin{aligned} \frac{2+4+6+\cdots+2014}{1+3+5+\cdots+2013}&=\frac{1+1+3+1+5+1+\cdots+2013+1}{1+3+5+\cdots+2013}\\&=\frac{1+3+5+\cdots+2013+\color{#3D99F6}{\boxed{1007}}}{1+3+5+\cdots+2013} \end{aligned}

Moderator note:

Nice. Can you generalize this?

Abdul Hadi Nafi
Aug 27, 2015

manual approach : if you follow the two series then its obvious that in every term there is a difference of 1. i.e .(2+4+6+..................)-(1+3+5+.............)=(2-1)+(4-3)+(6-5)+.............. so no. of terms of each series gives u the difference between this two series , which is the remainder . now, 1+(n-1)*2=2013 so , n =1007

Keshav Bassi
Aug 20, 2015

Formula for Sum of first n even numbers can be found using AP i.e. n(n+1) and similarly for odd numbers we have (n+1)^2. Using these formulae expressions can be simplified.

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