SEAMO X 2023 — Paper C — Grade 5–6 Question 1

For coprime positive integers $m,n$, $\left(\frac12+\cdots+\frac1{72}\right)\left(1+\frac12+\cdots+\frac1{71}\right)-\left(1+\frac12+\cdots+\frac1{72}\right)\left(\frac12+\cdots+\frac1{71}\right)=m/n$. Find $m+n$.