Roy Clinton’s mail-ordering business wants to measure the response time of its operators in taking customer orders over the phone. Clinton lists below the time recorded (in minutes) from five different samples of the ordering process with four customer orders per sample. He wants to determine the upper and lower range control chart limits.

APPROACH c Looking in Table S6.1 for a sample size of 4, he finds that D4 = 2.282 and D3 = 0.