Aus Online Mathematik Brückenkurs 1

The denominator in the expression has 10 as a common factor,

\displaystyle \frac{3}{2\cdot 10}+\frac{7}{5\cdot 10}-\frac{1}{10}\,,

and it is therefore sufficient to multiply the top and bottom of each fraction by the other factors in the denominators in order to obtain a common denominator,

\displaystyle \frac{3\cdot 5}{20\cdot 5}+\frac{7\cdot 2}{50\cdot 2}-\frac{1\cdot 5\cdot 2}{10\cdot 5\cdot 2}=\frac{15}{100}+\frac{14}{100}-\frac{10}{100}\,.

The lowest common denominator (LCD) is therefore 100, and the expression is equal to

\displaystyle \frac{15}{100}+\frac{14}{100}-\frac{10}{100}=\frac{15+14-10}{100}=\frac{19}{100}\,.