Question

A particular brand of tires claims that its deluxe tire averages at least 50,000 miles before it needs to be replaced. From past studies of this tire, the standard deviation is known to be 8,000. A survey of owners of that tire design is conducted. From the 28 tires surveyed, the mean lifespan was 46,500 miles with a standard deviation of 9,800 miles. Using alpha 0.05, is the data highly inconsistent with the claim?

Answer 1

p-value = 0.01044

Hence, P-value ( 0.01044 ) is less than level of significance ( 0.05 )

We reject H₀

Reject the claim that deluxe tires averages at least 50000 miles before it needs to be replaced.

∴ the data is highly inconsistent with the claim

Explanation:

Given the data in the question;

x' = 46500

σ = 8000

sample size n = 28

Null hypothesis H₀ : μ ≥ 50000

Alternative hypothesis H₁ : μ < 50000

level of significance ∝ = 0.05

Using Test statistics;

Z = [(x' - μ ) / (σ√n)] ~ (0,1)

we substitute

Z = [(46500 - 50000 ) / (8000√28)]

= -3500 / 1511.85789

= - 2.31

{ since alternative hypothesis is left tailed } from z-table;

p-value = P( z ≤ -2.32 )

p-value = 0.01044

Hence, P-value ( 0.01044 ) is less than level of significance ( 0.05 )

We reject H₀

Reject the claim that deluxe tires averages at least 50000 miles before it needs to be replaced.

∴ the data is highly inconsistent with the claim