Answer
$P(guessing~the~Social~Security~number~of~the\\~president~of~the~U.S.)=\frac{1}{1,000,000,000}=0.000000001$
Work Step by Step
The sample space: 1,000,000,000 Social Security numbers. So, N(S) = 1,000,000,000.
The president of the United States has one Social Security number. So, N(Social Security number of the president of the U.S.) = 1.
Using the Classical Method (see page 259):
$P(guessing~the~Social~Security~number~of~the\\~president~of~the~U.S.)=\frac{N(Social~Security~number~of~the~president~of~the~U.S)}{N(S)}=\frac{1}{1,000,000,000}=0.000000001$
