$\frac{2020×2019-2018×2019}{2018×2019+2020×7+2012}$
= $\frac{2019×(2020-2018)}{2018×2019+(2019+1)×7+2012}$
= $\frac{2019×2}{2018×2019+2019×7+7+2012}$
= $\frac{2019×2}{2018×2019+2019×7+2019}$
= $\frac{2019×2}{2019×(2018+7+1)}$
= $\frac{2019×2}{2019×2026}$
= $\frac{2}{2026}$ = $\frac{1}{1013}$