How long do new batteries last on a camping trip? A random sample of n1 = 42 small camp flashlights were installed with brand I batteries and left on until the batteries failed. The sample mean lifetime was x1 = 9.8 hours with sample standard deviation s1 = 2.2 hours. Another random sample of n2 = 38 small flashlights of the same model were installed with brand II batteries and left on until the batteries failed. The sample mean of lifetimes was x2 = 8.1 hours with sample standard deviation s2 = 3.5 hours.