[求助]问几道PREP的数学题，多谢大家

1 The figure（图案是个圆环，然后圆环图了颜色，不好意思，不会在帖子上面弄图案只能用描述了。） shows the top side of a
circular medallion made of colored glass surrouned by a metal frame, represented
by the shaded region. If the radius of medallion is r centimeters and width of
the metal frame is s centimeters, then in terms of s and r, what is the area of
the metal frame, in wquare meters?

答案是πs(2r-s) 

我对这道题的理解可能有问题，没有读懂题目说的是什么。

2 Mary bought several pencils. If each pencil was either a 23 cent pencil or
a 21cent pencil, howmany 23-pencil did M buy?

(1)M bought a total of 6 pencils. (2)The total value of pencils M bought is
130.

正确答案选B。我怎么觉得应该选C呢？因为如果只有第2个条件的话，列不出来2个方程啊？

3 A certain car average 25 miles per gallon when driven in the city and 40
miles per gallon when driven on the high way.Accoding to these raes, which of he
following is closest to the number of miles per gallon that the car average when
it is driven 10 miles in the city and then 50 miles on the high way ?

正确答案是36.   这道题我也是没有读懂题目。先谢谢大家的帮助。

60是总路程。60=10+50

第2题，用列举法比较容易拉

因为总得是130，所以他买得pencils最多只有6只，因为最低21×7＝147了

假使23 1支，因为130个位是0，那么21的应该7支，错

同里 :

23 2支，21应该4支，合理，对

23 3支，21应该1支，23×3 ＋ 21 不是130

后面就更没有可能了。所以B

注：我发现GMAC很喜欢考这种问题，就是给出貌似不够得条件，但是因为凑整，总能解决问题得。大家小心呀