Consider an x distribution with standard deviation = 45. (For each answer, enter an exact number.)

(a) If specifications for a research project require the standard error of the correspondingdistributionto be3, how large does the sample size need to be?

(b) If specifications for a research project require the standard error of the correspondingdistributionto be 1, how large does the sample size need to be?

Police response time to an emergency call is the difference between the time the call is first received by the dispatcher and the time a patrol car radios that it has arrived at the scene. Over a long period of time, it has been determined that the police response time has a normal distribution with a mean of 9.2 minutes and a standard deviation of 2.1 minutes. For a randomly received emergency call, find the following probabilities. (For each answer, enter a number. Round your answers to four decimal places.)

(c) the response time is between 5 and 11 minutes

(d) the response time is more than 11 minutes

Assume that x has a normal distribution with the specified mean and standard deviation. Find the indicated probability. (Enter a number. Round your answer to four decimal places.)

= 20; = 3.4

(e) P(x 30) =

Sketch the area under the standard normal curve over the indicated interval and find the specified area. (Enter a number. Round your answer to four decimal places.)

(f) The area to the left of z = 0.52 is