2-40 Armstrong Faber produces a standard number-twopencil called Ultra-Lite. Since Chuck Armstrongstarted Armstrong Faber, sales have grown steadily.With the increase in the price of wood products,however, Chuck has been forced to increase theprice of the Ultra-Lite pencils. As a result, the de-mand for Ultra-Lite has been fairly stable over thepast 6 years. On the average, Armstrong Faber hassold 457,000 pencils each year. Furthermore, 90%of the time sales have been between 454,000 and460,000 pencils. It is expected that the sales follow anormal distribution with a mean of 457,000 pencils.Estimate the standard deviation of this distribution.(Hint: Work backward from the normal table to findZ. Then apply Equation 2-13.)

It is given that Mean, μ = 457000 P( 454000 < X < 460000 ) = 90% = 0.90

sold 457,000 pencils each year. Furthermore, 90% of the time sales have been between 454,000 and 460,000 pencils. It is expected that the sales follow a normal distribution with a mean of 457,000 pencils. Estimate the standard deviation of this distribution. (Hint: Work backward from the normal table to find Z. Then apply Equation 2-13.)