Question 1178242
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    P = {{{C[4]^3/C[25]^4}}}.


The denominator  {{{C[25]^3}}} = {{{(25*24*23)/(1*2*3)}}} = 2300  is the number of all possible triples of 25 drivers.


It is the total set of events.



The numerator  {{{C[4]^3}}} = 4 is the number of favorable triples of the four Smith brothers.


It is the set of all favorable triples.



The ratio  P = {{{favorable/total}}} = {{{4/2300}}} = {{{1/575}}} = 0.001739 is the probability under the question.    <U>ANSWER</U>
</pre>


Solved, answered and explained.



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In the other form, this probability is  &nbsp;&nbsp;&nbsp;&nbsp;P = {{{(4/25)*(3/24)*(2/23)}}} = 0.001739,  &nbsp;&nbsp;which is the same number/answer.



The last formula may seem to be more self-explanatory to you . . .