Stock A pays 30% in a boom, 5% in a normal economy and -20% in a
recession. If we are equally likely to see a boom, a normal economy
and a recession next year, what is the standard deviation of the
one-year return on stock A? Enter your result as a percentage point
without the % sign, and round it to the second decimal point (i.e.,
if the answer is 10.3456%, enter it as 10.35).