document.write( "Question 1081612: The class average on a test is 85% with a standard deviation of 3%. Assuming that the marks are normally distributed, what mark range would 80% of the students fall within? \n" ); document.write( "

Algebra.Com's Answer #695688 by stanbon(75887) $\"\"$ $\"About$

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The class average on a test is 85% with a standard deviation of 3%. Assuming that the marks are normally distributed, what mark range would 80% of the students fall within?
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\n" ); document.write( "Sketch the picture.
\n" ); document.write( "You have a normal curve with p = 0.85 and s = 0.03
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\n" ); document.write( "Assuming you want the 80% to be centered on p = 0.85,
\n" ); document.write( "your have a left-tail of 10% and a right-tail of 10%.
\n" ); document.write( "left-tail z-value is invNorm(0.10) = -1.2816
\n" ); document.write( "right-tail z-value is invNorm(0.90) = +1.2816
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\n" ); document.write( "Find the corresponding mark values using x = z*s + p
\n" ); document.write( "Left-limit:: x = -1.2816*0.03+0.85
\n" ); document.write( "Right-limit:: x = +1.2816*0.03+0.85
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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