In a meeting, 70% of the members favour and 30% oppose a certain proposal. A member is selected at random and we take $X = 0$ if he opposed, and $X= 1$ if he is in favour. Then, $E (X)$ is:

$\frac{7}{10}$

$F$ → favour

$\overline F$ → oppose

$P(F) = 70\%=\frac{7}{10}$   $X=1$

$P(\overline F) = 30\%=\frac{3}{10}$   $X=0$

So, $E(X) = 0×\frac{3}{10}+1×\frac{7}{10}=\frac{7}{10}$