Chapter-8

1. A manufacturer makes street rods that are suppose to have a mean length of 50cm. A retailer suggests that the bars are running short (claim mean is less than 50) A sample of 41 bars is taken and the sample mean is 51 cm with a sample standard deviation (s) of 3.6 Test the retailers claim at the .01 level of significance---(t table) ( use z) 2. A test of sobriety involves measuring the subject's motor skills . Twenty randomly selected sober subjects take the test and produce a mean of 41. It is know the population standard deviation is 3.7. At the 0.01 level of significance , test the claim the true mean score for all sober subjects is equal to 35. Test this claim at the 0.05 level.

3. Has the proportion of Facebook accounts decreased worldwide? Many young adults believe this is the case because of several other media now taking center stage. In 2020, a report claimed 59% of social media users use Facebook. Suppose you conducted a survey of 48 people and it showed 23 have a Facebook account Use the .05 level of significance to determine whether the proportion of social media users who have a facebook account has decreased from 59%. (use z)