document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=733109>Question 733109</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Hello,<BR>\n" );
document.write( "If the probability of an event occuring is 10%, what is the probability that 2 or more times the event will occur in 30 , 40 or 50 trials. In the case of 30 trials I have been using the formula P(2 out of 30) = (30! / (2!*(30-2)!) *.01*(0.9*10^28). I get 22.7%. I think that I am calculating exactly 2 events occuring. How do I calculate at least 2 events?\r<BR>\n" );
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document.write( "Thanks.<BR>\n" );
document.write( "Ross </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #448278 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=448278\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> If the probability of an event occuring is 10%, what is the probability that 2 or more times the event will occur in 30 , 40 or 50 trials. In the case of 30 trials I have been using the formula P(2 out of 30) = (30! / (2!*(30-2)!) *.01*(0.9*10^28). I get 22.7%. I think that I am calculating exactly 2 events occuring. How do I calculate at least 2 events?<BR>\n" );
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document.write( "Binomial Problem with n = 30 and p(event) = 0.1<BR>\n" );
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document.write( "P(2<= x <=30) = 1 - [P(x = 0)+P(x=1)]<BR>\n" );
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document.write( "= 1 - [30C0(0.1)^0*0.9^30 + 30C1(0.1)^1*(0.9)^29]<BR>\n" );
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document.write( "Now using a TI-84 calculator:<BR>\n" );
document.write( "= 1 - binomcdf(30,0.1,1) = 0.8163<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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