Define a function $`$coin$\_$flip$($num$)`$ that flips a coin $N$ $($here $N$ is the same as $`$num$`)$ times, with probability $p$=0\mathrm{.}3$$ for heads $($$x$=1$$$)$ and probability $$1-$p$=0\mathrm{.}7$$ for tails $($$x$=0$$$),$ and returns $$\backslash$langle x $\backslash$rangle$$.$