Question

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

Answer 1

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.

Answer 2

@kropot72 @jim_thompson5910

Answer 3

I doubt it's D....

Answer 4

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

Answer 5

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)

Answer 6

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

Answer 7

np