Question 714642
<font face="Times New Roman" size="+2">


From the way you worded the question, I would presume that selecting none of the five choices is NOT an option, i.e., every random selection would include at least one of the choices "A" through "E".  In this case, your answer of 1/31 is spot on.  On the other hand, if not making any selection is a valid option for answering the question, the correct probability would be 1/32 because you would have to calculate:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \sum_{r=0}^5\,{{5} \choose {r}}\ =\ 1\ +\ 5\ +\ 10\ +\ 10\ +\ 5\ +\ 1\ =\ 32]


instead of 


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \sum_{r=1}^5\,{{5} \choose {r}}\ =\ 5\ +\ 10\ +\ 10\ +\ 5\ +\ 1\ =\ 31]


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
<font face="Math1" size="+2">Egw to Beta kai to Sigma</font>
My calculator said it, I believe it, that settles it
<div style="text-align:center"><a href="http://outcampaign.org/" target="_blank"><img src="http://cdn.cloudfiles.mosso.com/c116811/scarlet_A.png" border="0" alt="The Out Campaign: Scarlet Letter of Atheism" width="143" height="122" /></a></div>
</font>