Hi! I already answered a) and b) of these questions, but I can't seem to figure out c). I used chebychev's inequality. Here it is, with my answers:

An electrical firm manufactures 100-watt light bulbs. These bulbs, according to specifications written on the package, have a mean life of 900 hours with a standard deviation of 50 hours. Assume that the distribution is symmetric about the mean.

a) Give an upper bound to the probability that the life of a bulb win a new production batch will exceed 990 hours.

Screenshot 1:

Find k: u - ko = 990 - k = (990-900) = 1.8 50 P(u - ko 1 - 1 P(900 - 1.8 * 50 0.691 Because the distribution is symmetric about the mean, we can assume that the left tail P(0