Question Number 187044 by Humble last updated on 12/Feb/23
$${f}\left({x},{y}\right)=\left\{\left({x}+{y}\right),\mathrm{0}<{x}<\mathrm{1},\:\mathrm{0}<{y}<\mathrm{1}\right. \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\mathrm{0},\:{otherwise} \\ $$$${find}: \\ $$$$\left(\mathrm{1}\right)\:\sigma{xy} \\ $$$$ \\ $$$$\left(\mathrm{2}\right)\:\:{p}\left(\mathrm{0}<{x}<\left(\frac{\mathrm{1}}{\mathrm{4}}\right)\mid\left(\frac{\mathrm{2}}{\mathrm{5}}\right)>{y}>\left(\frac{\mathrm{1}}{\mathrm{3}}\right)\right) \\ $$$$ \\ $$$${note}:\:{f}\left({x},{y}\right)\:{is}\:{the}\:{joint}\:{PDF} \\ $$