Question 347515
<font face="Garamond" size="+2">


The probability of selling at least 3 is 1 minus the probability of selling exactly 1 plus the probability of selling exactly 2.  (There is actually a fallacy in your probability function since you don't have a finite probability > 0 that the store will sell 0 magazines).  The probability of selling at least 4 is 1 - (P(1) + P(2) + P(3)), so:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ P(\geq3)\ =\ 1\ -\ \left(\frac{1}{15}\ +\ \frac{2}{15}\right)\ =\ \frac{4}{5}]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ P(\geq4)\ =\ 1\ -\ \left(\frac{1}{15}\ +\ \frac{2}{15}\ +\ \frac{3}{15}\right)\ =\ \frac{3}{5}]


Cost of 3 magazines = *[tex \LARGE 3\ \times\ $1\ =\ $3]


Expected return on 3 magazines = *[tex \LARGE 3\ \times\ $2\ \times\ \frac{4}{5}\ =\ $4.80]


Profit on 3 = *[tex \LARGE 4.80 -\ 3\ =\ $1.80]


Cost of 4 magazines = *[tex \LARGE 4\ \times\ $1\ =\ $4]


Expected return on 3 magazines = *[tex \LARGE 4\ \times\ $2\ \times\ \frac{3}{5}\ =\ $4.80]


Profit on 4 = *[tex \LARGE 4.80 -\ 4\ =\ $0.80]



John
*[tex \LARGE e^{i\pi} + 1 = 0]
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>