The concrete canoe team does some analysis on their design and calculates that they need a compressive strength of 860 psi. They test several mix designs and chose one that has a sample mean of 900 psi with a standard error of the mean of 10 psi. The team wishes to be very conservative in their design and calculates a one-sided 99% confidence interval on the lower limit. What is this value?

Question

Elliot Barton

Engineering

24 November, 14:40

The concrete canoe team does some analysis on their design and calculates that they need a compressive strength of 860 psi. They test several mix designs and chose one that has a sample mean of 900 psi with a standard error of the mean of 10 psi. The team wishes to be very conservative in their design and calculates a one-sided 99% confidence interval on the lower limit. What is this value?

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Answers (1)

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Kolby Sheppard · Answer 1

874 psi

Explanation:

Given a sample mean (x') = 900,

and a standard error (SE) = 10

At 99% confidence, Z (critical) = 2.58

That gives 99% confidence interval as,

x' ± Z (critical) x SE = 900 ± 2.58 x 10

The value of the lower limit is,

900 - 25.8 = 874.2

≈ 874 psi