#### Answer

$\frac{10}{15} = \frac{4}{6}$
True

#### Work Step by Step

x is to y is the same as $\frac{x}{y}$
To determine if a proportion is true, we have to find if the cross products are equal.
The cross products of $\frac{a}{b}=\frac{c}{d}$ are $a \cdot d$ and $b \cdot c$.
Ten is to fifteen as four is to six is the same as $\frac{10}{15} = \frac{4}{6}$
This proportion is true because $10*6=4*15=60$