document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1133959>Question 1133959</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A national standard requires that public bridges over 20 feet in length must be inspected and rated every 2 years. The rating scale ranges from 0​ (poorest rating) to 9​ (highest rating). A group of engineers used a probabilistic model to forecast the inspection ratings of all major bridges in a city. For the year​ 2020, the engineers forecast that 9​% of all major bridges in that city will have ratings of 4 or below. Complete parts a and b.\r<BR>\n" );
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document.write( "a. Use the forecast to find the probability that in a random sample of 7 major bridges in the​ city, at least 3 will have an inspection rating of 4 or below in 2020.<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 #751225 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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/cgi-bin/show-face.mpl?user=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=751225\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Look at the probability 0, 1, 2 will have such an inspection rating, then subtract that from 1 to give the probability of having at least 3<BR>\n" );
document.write( "for 0, it is 0.91^7=0.517<BR>\n" );
document.write( "for 1 it is 7*0.91^6*0.09=0.358<BR>\n" );
document.write( "for 2 it is 7C2*0.91^5*0.09^2=9=0.106<BR>\n" );
document.write( "These three add to 0.981, so 1-0.981=0.019  ANSWER<BR>\n" );
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