document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=560851>Question 560851</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 4.	Elizabeth had a bad night and didn’t study for her English test. She is so stressed that she can’t remember anything about Oedipus Rex. Her test is 20 multiple choice questions with 5 possible answers each.  She has no choice but to guess on each question.<BR>\n" );
document.write( "a.	How many questions can Elizabeth expect to get correct by guessing?<BR>\n" );
document.write( "b.	What is the probability that she passes the test? (Her final grade is at least a 70.)<BR>\n" );
document.write( "c.	What is the probability that Elizabeth answers only 5 questions correctly?<BR>\n" );
document.write( "d.	What is the probability that she answers less than 10 questions incorrectly?<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #364067 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=364067\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Her test is 20 multiple choice questions with 5 possible answers each. She has no choice but to guess on each question.<BR>\n" );
document.write( "-----<BR>\n" );
document.write( "Binomial Problem with n = 20 and p(correct) = 1/5<BR>\n" );
document.write( "-------------------<BR>\n" );
document.write( "a. How many questions can Elizabeth expect to get correct by guessing?<BR>\n" );
document.write( "Ans: np = 20*(1/5) = 4<BR>\n" );
document.write( "-----------------------------<BR>\n" );
document.write( "b. What is the probability that she passes the test? (Her final grade is at least a 70.)<BR>\n" );
document.write( "P(14 <= x <= 20)) = 1 - binomcdf(20,0.2,13) = 0.000001845<BR>\n" );
document.write( "================================================================== <BR>\n" );
document.write( "c. What is the probability that Elizabeth answers only 5 questions correctly?<BR>\n" );
document.write( "P(x = 5) = 20C5(1/5)^5*(4/5)^15 = 0.1746<BR>\n" );
document.write( "-----------------------------------<BR>\n" );
document.write( "d. What is the probability that she answers less than 10 questions incorrectly?<BR>\n" );
document.write( "P(0<= x <= 9) = binomcdf(20,0.2,9) = 0.9861<BR>\n" );
document.write( "====================================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( "==============<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );