1. A producer specifies that the mean lifetime of a certain type of battery is at least 240 hours. A sample of 18 such batteries yielded the following data.
237 242 232
242 248 230
244 243 254
262 234 220
225 236 232
218 228 240
Assuming that the life of the batteries is approximately normally distributed, do the data indicate that the specifications are not being met?
2. A company supplies plastic sheets for industrial use. A new type of plastic has been produced and the company would like to claim that the average stress resistance of this new product is at least 30.0, where stress resistance is measured in pounds per square inch (psi) necessary to crack the sheet. The following random sample was drawn off the production line. Based on this sample, would the claim clearly be unjustified?
30.1 32.7 22.5 27.5
27.7 29.8 28.9 31.4
31.2 24.3 26.4 22.8
29.1 33.4 32.5 21.7
Assume normality and use the 5 percent level of significance.