Answer
$-\dfrac{1}{7}n^{2}+\dfrac{5}{12}m-\dfrac{7}{20}$
Work Step by Step
$\Big(-\dfrac{4}{7}n^{2}+\dfrac{5}{6}m-\dfrac{1}{20}\Big)+\Big(\dfrac{3}{7}n^{2}-\dfrac{5}{12}m-\dfrac{3}{10}\Big)$
Remove both parentheses:
$-\dfrac{4}{7}n^{2}+\dfrac{5}{6}m-\dfrac{1}{20}+\dfrac{3}{7}n^{2}-\dfrac{5}{12}m-\dfrac{3}{10}=...$
Simplify by combining like terms:
$...=\Big(\dfrac{3}{7}-\dfrac{4}{7}\Big)n^{2}+\Big(\dfrac{5}{6}-\dfrac{5}{12}\Big)m-\Big(\dfrac{1}{20}+\dfrac{3}{10}\Big)=...$
$...=-\dfrac{1}{7}n^{2}+\dfrac{60-30}{72}m-\dfrac{10+60}{200}=...$
$...=-\dfrac{1}{7}n^{2}+\dfrac{30}{72}m-\dfrac{70}{200}=...$
$...=-\dfrac{1}{7}n^{2}+\dfrac{5}{12}m-\dfrac{7}{20}$
