A study of tire pressure in brand new Toyotas used a sample size of 120 tires and reported a mean of 30.3 psi and a margin or er
ror of plus or minus 1.8 psi with 95% confidence. We may conclude that, with 95% confidence, the mean tire pressure of tires on new Toyota cars is between psi (lower number) and psi (higher number).
Since the question already provided the mean (30.3 psi) and the margin of error with confidence of 95% (+ or - 1.8 psi), simply add and subtract the margin of error to the mean value to find the confidence interval:
Lower bound:
L = 30.3 - 1.8 = 28.5
Upper bound:
H = 30.3 +1.8 = 32.1
Therefore, the mean tire pressure of tires on new Toyota cars is between 28.5 psi and 32.1 psi.
