COMPARISON OF SPECIALTY AUXILIARY BACKUP LAB BATTERY LIFETIMES

A company that manufactures specialty batteries used as auxiliary back- ups for sensitive laboratory equipments in need of constant power sup- plies claims that its new prototype, brand A, has a longer lifetime (un- der constant use) than the industry-leading brand B, and at the same cost. Using accepted industry protocol, a series of tests carried out in an independent laboratory produced the following results: For brand A: sample size, n1 = 40; average lifetime, x¯1 = 647 hrs; with a population standard deviation given as σ1 = 27 hrs. The corresponding results for brand B are n2 = 40; x¯2 = 638; σ2 = 31. Determine, at the 5% level, if there is a signi?cant difference between the observed mean lifetimes.