Lightning McQueen races with an average speed of 125 miles per hour. He drives 400 miles in a race, how much time does it take him to complete the race?

Please help 20 points

Asynthetic fiber used in manufacturing carpet has tensile strength that is normally distributed with mean 75.5 psi and standard deviation 3.5 psi. how is the standard deviation of the sample mean changed when the sample size is increased from n equals 8 to n equals 47