Question

For a normal population with known variance σ2 what value of z /α2 gives 98% confidence? a)1.15 b)2.33c)1.29d)1.96

Past experience has indicated that the breaking strength of yarn used in manufacturing drapery material is normally distributed and that σ = 2 psi. A random sample of nine specimens is tested, and the average breaking strength is found to be 98 psi. Find a 95% two-sided confidence interval on the true mean breaking strength. A) 96.7 ≤ μ ≤99.3, b)87.8 u93.1, c)75.7 u 83,0, d)97.6 u 98.7. A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally distributed with σ = 1000(psi)². A random sample of 12 specimens has a mean compressive strength of x = 3250 psi. It is desired to estimate the compressive strength with an error that is less than 15 psi at 99% confidence. What sample size is required? A) 29 B) 30 C) 17 D) 18

Answer 1