Question

A bag contains 7 black and 4 white balls two balls are drawn at a time from the bag. The probability at least one white ball is selected is

Answer 1

We can select 2 balls from 11 balls. This is the sample space of this experiment. Selecting two black balls from the seven black balls is the event we are intereseted in. So we get
\[
\begin{aligned}
&\mathrm{P}=1-\left[\dfrac{{ }^{7} \mathrm{C}_{2}} {{ }^{11}{\mathrm{C}_{2}}}\right] \\
&=\dfrac{34}{55}
\end{aligned}
\]