You measure the lifetime (in miles of driving use) of a random sample of 25 tires of a certain brand. The sample mean is 64,200 miles. Suppose that the lifetimes for tires of this brand follow a normal distribution, with unknown mean μ and standard deviation σ = 4,800 miles. A 95% confidence interval for μ is about

Question

konradzuse · Answer

A.	62,318.4 miles to 66,081.6 miles.
B.	62,620.8 miles to 65,779.2 miles.
C.	63,240 miles to 65,160 miles.
D.	54,792 miles to 73,608 miles.

konradzuse · Answer

@kropot72 @jim_thompson5910

konradzuse · Answer

I doubt it's D....

konradzuse · Answer

A nad B seem tobe too far also... I'm going to guess C?

jim_thompson5910 · Answer

95% Confidence Interval:


(  xbar - z(sigma/sqrt(n)),  xbar + z(sigma/sqrt(n))  )


(  64200 - 1.96(4800/sqrt(25)),  64200 + 1.96(4800/sqrt(25))  )


(  64200 - 1881.6 ,  64200 + 1881.6  )


(   62,318.4, 66,081.6)

konradzuse · Answer

Going to jot that formula down, thanks Jim I was wrong :P.

jim_thompson5910 · Answer

np