## Elementary Technical Mathematics

$\displaystyle \frac{1}{20}$
Apply the equivalent fractions rule, $\quad \displaystyle \frac{a}{-b}=\frac{-a}{b}=-\frac{a}{b}$ $\displaystyle \left(\frac{-1}{4} \right)\left(\frac{1}{-5} \right)$=$\displaystyle \left(-\frac{1}{4} \right)\left(-\frac{1}{5} \right)$ Multiplying two numbers with the same sign: Multiply their absolute values; the sign of the result is "+" $=+\displaystyle \frac{1}{4}\cdot\frac{1}{5}$ Multiply fractions: We have no common factors, so we multiply the numerators and place that product over the product of the denominators. $=\displaystyle \frac{1}{20}$