Big Corporation produces just about everything but is currently interested in the lifetimes of its batteries, hoping to obtain its share of a market boosted by the popularity of portable CD and MP3 players. To investigate its new line of Ultra batteries, BIG randomly selects 1000 ultra batteries and finds that they have a mean lifetime of 911 hours. Suppose that this mean applies to the population of all ultra batteries.

Complete the following statements about the distribution of lifetimes of all ultra batteries.

A.) According to Chebyshev's theorem, at least ______ of the lifetimes lie within 1.5 standard deviations of the mean, 911 hours.

B.) Suppose that the distribution is bell-shaped. If approximately 95% of the lifetimes lie between 723 hours and 1099 hours, then the approximate value of the standard deviation for the distribution, according to the empirical rule, is____