<PRE><B>Question 807050</B>
&lt;font face=&quot;Times New Roman&quot; size=&quot;+2&quot;&gt;


Your arithmetic is off a bit, as your calculation should have come up with -5.  But you are using the wrong Z-score formula anyway.  You get a Z-score of -5 against the proposition that you have a sample &lt;u&gt;mean&lt;/u&gt; of 15 across your sample of 25.  This is a much smaller probability than what is actually being asked for.  You just want the probability that a given invoice would be paid in 15 days, which is just the percentage of the general population that is 1 standard deviation below the mean, or Z = -1.000.  Just look it up.


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
&lt;font face=&quot;Math1&quot; size=&quot;+2&quot;&gt;Egw to Beta kai to Sigma&lt;/font&gt;
My calculator said it, I believe it, that settles it
&lt;div style=&quot;text-align:center&quot;&gt;&lt;a href=&quot;http://outcampaign.org/&quot; target=&quot;_blank&quot;&gt;&lt;img src=&quot;http://cdn.cloudfiles.mosso.com/c116811/scarlet_A.png&quot; border=&quot;0&quot; alt=&quot;The Out Campaign: Scarlet Letter of Atheism&quot; width=&quot;143&quot; height=&quot;122&quot; /&gt;&lt;/a&gt;&lt;/div&gt;
&lt;/font&gt;</PRE>