\(\frac{5}{10}*\frac{10}{40}=\frac{50}{400}\)
\(\frac{2}{8}*\frac{2}{4}=\frac{4}{32}\)
\(\frac{1}{4}*\frac{1}{2}=\frac{1}{8}\)
\(\frac{1}{8}\) is obtained by multiplying \(\frac{1}{2}\) and \(\frac{1}{4}\)
You basically create equivelant fractions for both 1/2 and 1/4 and multiply by each other. This way you get the same result always.
