请教PREP解题思路

dream_piggy

PREP－2 /

76.  

A hiker walking at a constant rate of 4 miles per hour is passed by a cyclist traveling in the same direction along the same path at a constant rate of 20 miles per hour.  The cyclist stops to wait for the hiker 5 minutes after passing her, while the hiker continues to walk at her constant rate.  How many minutes must the cyclist wait until the hiker catches up?

 

 

(A) 

(B) 15

(C) 20

(D) 25

(E) 

算来算去也没得出答案D,不知道是不是思路出了问题,请NN们指点

PREP-1/

117.

A certain office supply store stocks 2 sizes of self-stick notepads, each in 4 colors:  blue, green, yellow, or pink.  The store packs the notepads in packages that contain either 3 notepads of the same size and the same color or 3 notepads of the same size and of

3 different colors.  If the order in which the colors are packed is not considered, how many different packages of the types described above are possible?

 

 

(A)  6

(B)  8

(C)  16

(D)  24

(E)  32

这道题也是看得很晕,either 3 notepads of the same size and the same color指相同的尺寸和颜色--在本题中是不是可能性为零; 然后or 3 notepads of the same size and of

3 different colors就是C2/1*C4/3,这样算出来是8种,不过答案是C,搞不明白了

3 different colors就是C2/1*C4/3,这样算出来是8种,不过答案是C,搞不明白了

3 different colors就是C2/1*C4/3,这样算出来是8种,不过答案是C,搞不明白了

dream_piggy

明白啦，主要还是理解的问题。楼上的很强哦，以后要多多请教啦。

以前考GRE数学是满分的，现在PREP数学模考老是49也上不了50，不知道怎么办了

Economics

1骑车人超过走路人后，过了5分钟才停下来。题目就是问走路人走完骑车人5分钟内完

成的路程要用多少时间。

2同种颜色同种大小 same size and the same color； 不同颜色同种大小same size and of

3 different colors

dream_piggy

谢谢楼上的。再请教一下：

1, 先算骑车的人在5分钟之内走了多少路20*(5/60)=5/3 mile

题干中说The cyclist stops to wait for the hiker 5 minutes after passing her, while the hiker continues to walk at her constant rate，既然CYCLIST停下来等HIKER，为什么要算5分钟内走的路程呢

2. 同种颜色同种大小共有4+4=8, 这个式子怎么解释either 3 notepads of the same size and the same color ，能不能再明确说明一下

Economics

1, 先算骑车的人在5分钟之内走了多少路20*(5/60)=5/3 mile

   在算走路的人走同样多的路用多少时间(5/3)*1/4=5/12小时

   换算成分钟(5/12)*60=25 分钟。

2. 同种颜色同种大小共有4+4=8   再加上不同颜色同种大小2C43=8，一共8+8=16