document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=115381>Question 115381</A>: <I><SPAN STYLE=\"word-break: break-all;\"> This is homework and I have tried I keep coming up with 35 as the answer but different formulas each time......can someone show me the way with this one I am pulling my hair out\r<BR>\n" );
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document.write( "I= 50% II= 40% EXACTLY III= 35% = this is what I come up with and I do not think this is right because of the formula...statistics has formulas and this isn't one of them<BR>\n" );
document.write( "This is the problem:\r<BR>\n" );
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document.write( "There are 20 questions in a multiple-choice test. Each question has five <BR>\n" );
document.write( "choices and one correct answer out of these five choices. A student did not study. He/she answers the questions at random. What are the probability that he/she makes (i) more than 10 answer right? (ii) exactly eight right? (iii) at most 7 right? \r<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #84126 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=84126\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> There are 20 questions in a multiple-choice test. Each question has five <BR>\n" );
document.write( "choices and one correct answer out of these five choices. A student did not study.<BR>\n" );
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document.write( "Five choices means P(correct answer) = 1/5; P(wrong answer) = 4/5<BR>\n" );
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document.write( "The problem is binomial because the student either gets each answer<BR>\n" );
document.write( "correct or gets it wrong.<BR>\n" );
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document.write( "Let \"x\" be the number of correct answers.<BR>\n" );
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document.write( " He/she answers the questions at random. <BR>\n" );
document.write( "What are the probability that he/she makes <BR>\n" );
document.write( "(i) more than 10 answer right?<BR>\n" );
document.write( "P(x>10) = 1 - binomcdf(20,1/5,10) = 0.00056.. <BR>\n" );
document.write( "(ii) exactly eight right? <BR>\n" );
document.write( "P(x=8) = 20C8(1/5)^8(4/5)^12 = 125970*(2.56*10^-6)(0.068719...)=0.022<BR>\n" );
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document.write( "You could also use P(x=8)= binompdf(20,1/5,8) = 0.02216...<BR>\n" );
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document.write( "(iii) at most 7 right? <BR>\n" );
document.write( "P(0<=x<=7) = binomcdf(20,1/5,7) = 0.9678....<BR>\n" );
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document.write( "Comment:  The \"binompdf\" and \"binomcdf\" are functions on the TI-83 <BR>\n" );
document.write( "graphing calculator for determining binomial probabilities.<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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