A manufacturer claims that the life span of its tires is 48,000 miles. You work for a consumer protection agency

and you are testing these tires. Assume the life spans of the tires are normally distributed. You select 100 tires at random and test them. The mean life span is 47,772 miles. Assume σ=900. Complete parts​ (a) through​ (c).

​(a) Assuming the​ manufacturer’s claim is​ correct, what is the probability that the mean of the sample is 47,772 miles or​ less?

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