1.The National Transportation Safety Board (NTSB) wants to examine the safety of compact cars, midsize cars, and full-size cars. The pressures applied to the drivers' heads for each type of cars during crashes are shown.

Compact cars	Midsize cars	Full-size cars
643	469	484
655	427	453
702	525	402
	480	450
	500

a) ata = 0.05, test whether the mean pressure applied to the driver's head during a crash test is equal for each type of cars.

b) If there is a difference, test where the difference lies.