[求助]求救:三道有关数学的结论题

小孩laetitia

求救:三道有关数学的结论题(是刘向东逻辑分类练习里归纳题的30,33,35)

30.A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers,80 percent were not wearing seat belts at the time of their accidents.This indicates that, by wearing sear belts,drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.

The conclusion above is not properly drawn unless which of the following is true?

(A)Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing sear belts at the time of their accidents.

33.Recent estimates predict that between 1982 and 1995 the greatest increase in the number of people employed will be in the category of low-paying service occupations.This category, however, will not increase its share of total employment, whereas the category of high-paying service occupations weill increase its share.

If the estimates above are accurate,which of the following conclusions can be drawn?

(A) In 1982 more people were working in low-paying service occupations than were working in high-paying service occupations.

35. Corporate offices and directors commonly buy and sell, for their own portfolios, stock in their own corporations.Generally, when the ratio of such inside sales to inside purchases falls bellow 2 to 1 for a given stock, a rise in stock prices is imminent. In recent days, while the price of MEGA Corporation stock has been falling, the corporation's offices and directors have bought up to nine times as much of it as they have sold.

The facts above best support which of the following predictions?

(c)The price of MEGA stock will soon begin to go up.

感谢各位nn赐教