A phone manufacturer would like to test the battery capabilities of their new phones by playing a video on loop and measuring how much time it takes for the phones to run out of battery. Sixty phones underwent these tests, and it was found out that they run of juice on an average of 505.0 minutes with a sample standard deviation of 6.7 minutes. With a confidence level of 99 percent, solve for the confidence interval to estimate the population mean. Given:
Solutions:

An automobile assembly line operation has a scheduled mean completion time, μ, of 12 minutes. the standard deviation of completion times is 1.6 minutes. it is claimed that, under new management, the mean completion time has decreased. to test this claim, a random sample of 33 completion times under new management was taken. the sample had a mean of 11.2 minutes. assume that the population is normally distributed. can we support, at the 0.05 level of significance, the claim that the mean completion time has decreased under new management? assume that the standard deviation of completion times has not changed.

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9

Pls math have no ideamultiply and simppify. 2x^2y^3z^2 • 4xy^4x^2