$$ height\ of\ triangle=8\ squares $$

$$ length \ of\ triangle=10\ squares $$

$$ =>Area \ of\ triangle=\frac{8\times10}{2}=40 $$

By counting the unshaded squares, we will know that:

$$ unshaded\ squares=28 $$

$$ =>shaded\ squares=40-28=12 $$

$$ \therefore \frac{shaded}{unshaded}=\frac{12}{28}=\frac{3}{7} $$