document.write( "Question 235541: A car battery manufacturer introduces a new technique to increase the life of the battery. 25 batteries were tested and got a mean life of 4.6 years with a standard deviation of 0.70 years. Construct a 90% confidence interval for the mean life of the new battery.
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Algebra.Com's Answer #173555 by stanbon(75887)\"\" \"About 
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A car battery manufacturer introduces a new technique to increase the life of the battery. 25 batteries were tested and got a mean life of 4.6 years with a standard deviation of 0.70 years. Construct a 90% confidence interval for the mean life of the new battery.
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\n" ); document.write( "x-bar = 4.6 yrs.
\n" ); document.write( "standard error = E = 1.645*0.7/sqrt(25) = 0.2303
\n" ); document.write( "Comment: Since you want 90% confidence you build 45% on each
\n" ); document.write( "side of the mean. That leaves 5% in each of the tails. The
\n" ); document.write( "z-value border for that 5% tail is 1.645 as you can get using
\n" ); document.write( "your z-chart or calculator. I used a TI calculator to get
\n" ); document.write( "invNorm(0.95) = 1.645.
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\n" ); document.write( "90% CI: 4.6-0.2303 < u < 4.6+0.2303
\n" ); document.write( "90% CI: 4.3697 < u < 4.8303
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H. \n" ); document.write( "
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