## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$\dfrac{1}{6}$
We know that probability$=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}.$ Since there are $5$ white marbles and $5 + 10 + 8 + 7 = 30$ marbles in total, then $P(\text{white marble})=\dfrac{5}{30}=\dfrac{1}{6}$