2017 is 2 years old

Algebra Level 2

Determine the value of 2016 1 + 2015 2 + 2014 3 + + 1 2016 1 2 + 1 3 + 1 4 + + 1 2017 \large \frac{\frac{2016}{1} + \frac{2015}{2} + \frac{2014}{3} + \cdots + \frac{1}{2016}}{\frac{1}{2} + \frac{1}{3} + \frac{1}{4} + \cdots + \frac{1}{2017}}


The answer is 2017.

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3 solutions

Chew-Seong Cheong
Feb 26, 2019

Q = 2016 1 + 2015 2 + 2014 3 + + 1 2016 1 2 + 1 3 + 1 4 + + 1 2017 = 2017 1 1 + 2017 2 2 + 2017 3 3 + + 2017 2016 2016 1 2 + 1 3 + 1 4 + + 1 2017 = 2017 ( 1 1 + 1 2 + 1 3 + + 1 2016 ) 2016 1 2 + 1 3 + 1 4 + + 1 2017 = 2017 ( 1 2 + 1 3 + + 1 2016 ) + 1 1 2 + 1 3 + 1 4 + + 1 2017 = 2017 ( 1 2 + 1 3 + + 1 2016 + 1 2017 ) 1 2 + 1 3 + 1 4 + + 1 2017 = 2017 \begin{aligned} Q & = \frac {\frac {2016}1+\frac {2015}2 + \frac {2014}3+\cdots + \frac 1{2016}}{\frac 12 + \frac 13+\frac 14 + \cdots + \frac 1{2017}} \\ & = \frac {\frac {2017-1}1+\frac {2017-2}2 + \frac {2017-3}3+\cdots + \frac {2017-2016}{2016}}{\frac 12 + \frac 13+\frac 14 + \cdots + \frac 1{2017}} \\ & = \frac {2017 \left(\frac 11+\frac 12 + \frac 13+\cdots + \frac 1{2016}\right) - 2016}{\frac 12 + \frac 13+\frac 14 + \cdots + \frac 1{2017}} \\ & = \frac {2017 \left(\frac 12 + \frac 13+\cdots + \frac 1{2016}\right) + 1}{\frac 12 + \frac 13+\frac 14 + \cdots + \frac 1{2017}} \\ & = \frac {2017 \left(\frac 12 + \frac 13+\cdots + \frac 1{2016} + \frac 1{2017} \right)}{\frac 12 + \frac 13+\frac 14 + \cdots + \frac 1{2017}} \\ & = \boxed{2017} \end{aligned}

Meet Patel
Feb 26, 2019

Notice that 2016 1 + 2015 2 + + 1 2016 = 2017 ( 1 + 1 2 + 1 3 + + 1 2016 ) 2016 = 2017 ( 1 2 + 1 3 + 1 4 + + 1 2017 ) \frac{2016}{1} + \frac{2015}{2} + \dots + \frac{1}{2016} = 2017 \left(1 + \frac{1}{2} + \frac{1}{3} + \dots + \frac{1}{2016} \right) - 2016 = 2017 \left( \frac{1}{2} + \frac{1}{3} + \frac{1}{4} + \dots + \frac{1}{2017} \right) Therefore, the conclusion holds.

Kyle T
Feb 26, 2019

<?php
$n=0;
$d=0;
for($i=1;$i<2017;$i++){
$n += (2017-$i)/$i;
$d += 1/($i+1);
}
echo $n/$d; //prints 2017
?>




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