Three coins are tossed simultaneously. Consider the event $E$ ' three heads or three tails', $\mathrm{F}$ 'at least two heads' and $\mathrm{G}$ ' at most two heads '. Of the pairs $(E,F)$, $(E,G)$ and $(F,G)$, which are independent? which are dependent ?

The sample space of the experiment is given by

Clearly      $\mathrm{S}=\{\mathrm{HHH}, \mathrm{HHT}, \mathrm{HTH}, \mathrm{THH}, \mathrm{HTT}, \mathrm{THT}, \mathrm{TTH}, \mathrm{TTT}\}$

$\mathrm{E}=\{\mathrm{HHH}, \mathrm{TTT}\}, \mathrm{F}=\{\mathrm{HHH}, \mathrm{HHT}, \mathrm{HTH}, \mathrm{THH}\}$

and        $\mathrm{G}=\{\mathrm{HHT}, \mathrm{HTH}, \mathrm{THH}, \mathrm{HTT}, \mathrm{THT}, \mathrm{TTH}, \mathrm{TTT}\}$

Also       $\mathrm{E} \cap \mathrm{F}=\{\mathrm{HHH}\}, \mathrm{E} \cap \mathrm{G}=\{\mathrm{TTT}\}, \mathrm{F} \cap \mathrm{G}=\{\mathrm{HHT}, \mathrm{HTH}, \mathrm{THH}\}$

Therefore  $\mathrm{P}(\mathrm{E})=\frac{2}{8}=\frac{1}{4}, \mathrm{P}(\mathrm{F})=\frac{4}{8}=\frac{1}{2}, \mathrm{P}(\mathrm{G})=\frac{7}{8}$

and          $\mathrm{P}(\mathrm{E} \cap \mathrm{F})=\frac{1}{8}, \mathrm{P}(\mathrm{E} \cap \mathrm{G})=\frac{1}{8}, \mathrm{P}(\mathrm{F} \cap \mathrm{G})=\frac{3}{8}$

Also       $\mathrm{P}(\mathrm{E}) \cdot \mathrm{P}(\mathrm{F})=\frac{1}{4} \times \frac{1}{2}=\frac{1}{8}, \mathrm{P}(\mathrm{E}) \cdot \mathrm{P}(\mathrm{G})=\frac{1}{4} \times \frac{7}{8}=\frac{7}{32}$

and        $\mathrm{P}(\mathrm{F}), \mathrm{P}(\mathrm{G})=\frac{1}{2} \times \frac{7}{8}=\frac{7}{16}$

Thus      $\mathrm{P}(\mathrm{E} \cap \mathrm{F})=\mathrm{P}(\mathrm{E}) \cdot \mathrm{P}(\mathrm{F})$

$\mathrm{P}(\mathrm{E} \cap \mathrm{G}) \neq \mathrm{P}(\mathrm{E}) \cdot \mathrm{P}(\mathrm{G})$

and      $\mathrm{P}(\mathrm{F} \cap \mathrm{G}) \neq \mathrm{P}(\mathrm{F}) \cdot \mathrm{P}(\mathrm{G})$

Hence, the events $(E$ and $F)$ are independent, and the events $(E$ and $G)$ and $(F$ and $G) $ are dependent.