1. CONFIDENCE INTERVALS FOR MEANS

The mean and standard deviation of the maximum loads supported by 60 cables (see Problem 3.59) are given by 11.09 tons and 0.73 ton, respectively. Find the (a) 95% and (b) 99% confidence limits for the mean of the maximum loads of all cables produced by the company.

2. The mean and standard deviation of the diameters of a sample of 250 rivet heads manufactured by a company are 0.72642 in and 0.00058 in, respectively (see Problem 3.61). Find the (a) 99%, (b) 98%,

(c) 95%, and (d ) 90% confidence limits for the mean diameter of all the rivet heads manufactured by the company.

3. If the standard deviation of the lifetimes of television tubes is estimated to be 100 h, how large a sample must we take in order to be (a) 95%, (b) 90%, (c) 99%, and (d ) 99.73% confident that the error in the estimated mean lifetime will not exceed 20 h?

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