求教一道kaplan数学题

snowflowers

At Airport Z, 40 percent of airplanes are domestically owned, and 50 percent of the airplances have been in service at least 2 years. If 30 percent of the airplanes with at least 2 years services are long-distance carriers, how many of the airplanes that have been in service at least 2 years are long-distance carriers?

(1) Exactly  200 of the airplanes are domestically owned.

(2) Of the aircraft with less than 2 years of service, 40 percent are long-distance carriers.

ANS is A. I don't get it. NN please help me out...Thanks.

aprilhuang

total airplanes= 200/40%=500

and 50% of total airplanes have been in service at least 2 yrs =500/2=250

30 of the above airplanes are long-distance carriers =30%*250=75 so condition A is OK

condition 2 leads nothing to the question only focus on the long distance airplane which had been at least 2 years. But condition 2 is talking about the precentage of plane less than 2 years.

snowflowers

oh yeah. Thanks!