Answer
$\frac{17}{20}$
Work Step by Step
The LCM of the original denominators, 5, 10, and 20, is 20. Therefore, we can rewrite all three fractions with a denominator of 20.
$\frac{3}{10}+\frac{2}{5}+\frac{3}{20}=\frac{3\times2}{10\times2}+\frac{2\times4}{5\times4}+\frac{3}{20}=\frac{8}{20}+\frac{6}{20}+\frac{3}{20}=\frac{8+6+3}{20}=\frac{17}{20}$
