document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=454467>Question 454467</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 9)	The time spent by students on a particular E270 homework assignment follows a normal distribution with a mean &#956; = 150 minutes and standard deviation &#963; = 40 minutes.  Then 90% of student finish the assignment within ± _____ minutes from the mean time period.								<BR>\n" );
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document.write( "a	41.6								<BR>\n" );
document.write( "b	51.2								<BR>\n" );
document.write( "c	65.6								<BR>\n" );
document.write( "d	78.6								<BR>\n" );
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document.write( "10)	On a different homework assignment the standard deviation of the time spent is 30 minutes.  If 20% of students finish the assignment under 115 minutes, then the mean time spent on this assignment is _____ minutes.								<BR>\n" );
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document.write( "a	157								<BR>\n" );
document.write( "b	153								<BR>\n" );
document.write( "c	146								<BR>\n" );
document.write( "d	140								<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 #312137 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=312137\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The time spent by students on a particular E270 homework assignment follows a normal distribution with a mean &#956; = 150 minutes and standard deviation &#963; = 40 minutes. Then 90% of student finish the assignment within ± _____ minutes from the mean time period.<BR>\n" );
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document.write( "Draw the picture of a normal curve.<BR>\n" );
document.write( "Center 90% around the mean.<BR>\n" );
document.write( "That leaves a right and a left tail or 5%.<BR>\n" );
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document.write( "The z-value cutoffs are +/-1.645<BR>\n" );
document.write( "The corresponding minute values are:<BR>\n" );
document.write( "x = 1.645*40 = 65.8 minutes<BR>\n" );
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document.write( "a 41.6 <BR>\n" );
document.write( "b 51.2 <BR>\n" );
document.write( "c 65.6 <BR>\n" );
document.write( "d 78.6<BR>\n" );
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document.write( "10) On a different homework assignment the standard deviation of the time spent is 30 minutes. If 20% of students finish the assignment under 115 minutes, then the mean time spent on this assignment is _____ minutes.<BR>\n" );
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document.write( "Find the z-value with a 20% left tail.<BR>\n" );
document.write( "z = -0.8416<BR>\n" );
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document.write( "Using x = zs+u<BR>\n" );
document.write( "115 = -0.8416*30 + u<BR>\n" );
document.write( "u = 115 + 25.25<BR>\n" );
document.write( "u = 140.25 mminutes<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
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document.write( "a 157 <BR>\n" );
document.write( "b 153 <BR>\n" );
document.write( "c 146 <BR>\n" );
document.write( "d 140 \r<BR>\n" );
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