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Statistics Math Question - Please teach me how to do this problem!?

THe ISA Babcock Company supplies poultry farmers with hens, advertising that a matyre B300 Layer hen prodyces eggs with a mean weight of 60.3 grams. Suppose that egg weights follow a Normal model with standard deviation 3.1 grams. a. What percent of the eggs produced by these hens weigh more than 61.5 grams? b. What is the probability that 18 randomly selected eggs average more than 61.4 grams?

Public Comments

1. First, convert the egg weight to a z-score: z = (61.5 - 60.3) / 3.1 = .39 Now you need to use a normal table, or z-table, usually located in your textbook. Look up a z-score of .39. Some z-tables are set up differently, but I will assume that your table will give you the area under the normal curve to the LEFT of z. I get an area of .6517, but we need the area to the RIGHT of z because the question used the phrase "more than". Therefore, the answer to part A is 1 - .6517, or .3483. If you have a TI-83/84, you could also press 2ND, DISTR, normalcdf(.39, 10), then ENTER. The "10" is just a large z-score...you could use 100 and get the same answer. With part B, the process is the same except that the standard deviation isn't 3.1, it's 3.1/sqrt(18).