Consider an um containing a large number of coins and suppose that each of the coins has some probability $p$ of turning up heads when it is flipped. However, this value of $p$ varies from coin to coin. Suppose that the composition of the um is such that if a coin is selected at random from the urn, then its $p$-value can be regarded as being the value of a random variable that is uniformly distributed over $[0,1]$. If a coin is selected at random from the urn and flipped twice, compute the probability that
(a) the first flip is a head;
(b) both flips are heads.