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E how many samples would have to be taken to ensure a

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Unformatted text preview: (3.78 ­2.967)2+(3.63 ­2.967)2+(3.21 ­2.967)2+(2.57 ­2.967)2+    (3.44 ­2.967)2+(2.49 ­2.967)2⦌ =2.89361/9 =0.3215  Sothesamplestandarddeviation,S=0.567  3/6 CEE 202 – Engineering Risk & Uncertainty Spring 2011 (Bond) Homework 9 Expected Values; Sampling 4) Steel rebar is fabricated with a mean tensile strength of 65 ksi and a standard deviation of 4.2 ksi. 51 samples are taken from the manufacturer’s warehouse. a) What is the expected value of the sample mean? b) What is the standard deviation of the sample mean? c) What is the probability that the sample mean will lie below 64 ksi? d) There is a 95% probability that the sample standard deviation will lie between what two values? e) How many samples would have to be taken to ensure a 90% probabi...
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