試題詳解

277. In a study of driver safety, drivers were categorized according to three risk factors. Exactly 1000 drivers exhibited each individual risk factor. Also, for each of the risk factors, there were exactly 400 drivers exhibiting that risk factor and neither of the other two risk factors. Finally, there were exactly 300 drivers who exhibited all three risk factors and 500 who exhibited none of the three risk factors.
.
Calculate the number of drivers in the study.
(A) 2000
(B) 2300
(C) 2450
(D) 2750
(E) 3500