A man cycles 12km to school every day at an average speed of 20km/h. On one particular day he cycled for a while, but then for a puncture. He walked the rest of the way at 4km/h. It took him an hour to get to school that day. How far did he walk?

The first-serve percentage of a tennis player in a match is normally distributed with a standard deviation of 4.3%. if a sample of 15 random matches of the player is taken, the mean first-serve percentage is found to be 26.4%. what is the margin of error of the sample mean? a. 0.086% b. 0.533% c. 1.11% d. 2.22%