Question

The manufacturer of the X-15 steel-belted radial truck tire claims that the mean mileage the tire can be driven before the tread wears out is 70,000 miles. Assume the mileage wear follows the normal distribution and the population standard deviation of the distribution is 4,000 miles. Crossett’s Truck Company bought 49 tires and found that the mean mileage for its trucks is 72,000 miles. is Crossett’s experience is different from that claimed by the manufacturer at the 0.01 significance level

Answer 1

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Ho: Mu = 70000 ( Claim)

Ha: Mu !=70000

Z = (Xbar-Mu)/(Stdev/sqrt(n)) = (72000-70000)/(4000/sqrt(49)) = 3.5

Now, P(|Z| > 3.5) = 0.000465

So, since p-value of 0.000465 is less than alpha = .01, we reject Ho and conclude that  manufacturer of the X-15 steel-belted radial truck tire claims that the mean mileage the tire can be driven before the tread wears out is 70,000 miles is FALSE