Chapter 11, Problem 2CP

Meticulous Drill & Reamer (MD&R) specializes in drilling and boring precise holes in hard metals (e.g., steel alloys, tungsten carbide, and titanium). The company recently contracted to drill holes with 3-centimeter diameters in large carbon-steel alloy disks, and it will have to purchase a special drill to complete this job. MD&R has eliminated all but two of the drills it has been considering: Davis Drills’ T2005 and Worth Industrial Tools’ AZ100. These producers have each agreed to allow MD&R to use a T2005 and an AZ100 for one week to determine which drill it will purchase. During the one-week trial, MD&R uses each of these drills to drill 31 holes with a target diameter of 3 centimeters in one large carbon-steel alloy disk, then measures the diameter of each hole and records the results. MD&R’s results are provided in the table that follows and are available in the DATAfile named MeticulousDrills.

MD&R wants to consider both the accuracy (closeness of the diameter to 3 centimeters) and the precision (the variance of the diameter) of the holes drilled by the T2005 and the AZ100 when deciding which model to purchase.

Managerial Report

In making this assessment for MD&R, consider the following four questions:

1. 1. Are the holes drilled by the T2005 or the AZ100 more accurate? That is, which model of drill produces holes with a mean diameter closer to 3 centimeters?
2. 2. Are the holes drilled by the T2005 or the AZ100 more precise? That is, which model of drill produces holes with a smaller variance?
3. 3. Conduct a test of the hypothesis that the T2005 and the AZ100 are equally precise (that is, have equal variances) at a = .05. Discuss your findings.
4. 4. Which drill do you recommend to MD&R? Why?