Welcome 2016! Part 20
Algebra
Level
4
\[\large \dfrac{1}{1+2}+\dfrac{1}{1+2+3}+\cdots+\dfrac{1}{1+2+\cdots+20}\]
If the value of the expression above is equal to \( \dfrac mn\), where \(m\) and \(n\) are coprime positive integers, find the value of \(m+n\).
by
Anish Harsha