The standard deviation of the lifetime of a particular brand of car battery is 4.3 months. a random sample of 10 of these batteries is taken. assuming that the lifetimes of all batteries of this brand are normally distributed, what is the probability that the mean lifetime for this sample is within 1 mouth of the mean lifetime for all batteries of this brand?
a. 0.019
b. 0.184
c. 0.519
d. 0.538
e. 0.769