[求助] 几道数学题

Henrik

A magazine subscription is offered for 1 year at $12 or for 3 years at $29. If the rates do not change during the 3 years, the cost of a 3-year subscriptions is appromixately what percent less than the total cost of 3 annual subscriptions?

Answer: 16%    可我怎么算都是19%.

On a legislative committee, the number of males is 2 fewer than twice the number of females. If one male was replaced by a female, there would be an equal number of males and females on the committee. How many member sare on the committee?

我列了两个方程 m+2=2f, m-1=f+1, 然后我算的结果是10, 但正确答案是9.

DS   Town T has 20000 residents, 60 percent of whom are female. what percent of the residents were born in Town T?

1)The number of female residents who wre born in Town T is twice the number of male residents who were not born in Town T.

2)The number of female residents who wre not born in Town T is twice the number of female residents who were born in Town T.

答案是不是C?

If a motorist had driven 1 hour longer on a certain day an dat an average rate of 5 mile sper hour faster, he would hav ecovered 70 more mile than he actually did. How many more mile swould he have covered than he actually did if he had driven 2 hours longer and at an avrage rate of 10 miles per hour faster on that day?

A 100

B 120

C140

D150

E Cannot be determined.

 

谢谢

Henrik

有牛人帮忙解答一下吗? 实在是想不明白啊.

Henrik

帮忙看一下啦