SI. 3 One ball is taken at random from a bag containing $(b-4)$ white balls and $(b+46)$ red balls. If $\frac{c}{6}$ is the probability that the ball is white, find $c$.
There are 50 white balls and 100 red balls.
$$
\begin{array}{l}
\mathrm{P}(\text { white ball })=\frac{50}{150}=\frac{1}{3}=\frac{2}{6}=\frac{c}{6} \\
\Rightarrow c=2
\end{array}
$$