请教两道数学题~~~

xrbear57

1. 图我就不传了，就是个半圆形的，但是这个半圆形下面写的是20ft

The figure above shows the dimensions of a semicircular cross section of a one-way tunnel.  The single traffic lane is 12 feet wide and is equidistant from the sides of the tunnel.  If vehicles must clear the top of the tunnel by at least ½ foot when they are inside the traffic lane, what should be the limit on the height of vehicles that are allowed to use the tunnel?


A.    5½ ft            B.    7½ ft         C.    8 ½ ft           D.    9½ ft       E.     10 ft
Q23:

AMOUNT OF BACTERIA PRESENT

Time	Amount
1:00 P.M.	10.0 grams
4:00 P.M.	x grams
7:00 P.M.	14.4 grams

Data for a certain biology experiment are given in the table above.  If the amount of bacteria present increased by the same fraction during each of the two 3-hour periods shown, how many grams of bacteria were present at 4:00 P.M.?  



A.    12.0

B.    12.1

C.    12.2

D.    12.3

E.     12.4

Answer:  

请问two 3-hour怎么理解啊？

我直接用（10+14.4）/2=12.2  但是答案是A。。





Q23:

AMOUNT OF BACTERIA PRESENT

Time	Amount
1:00 P.M.	10.0 grams
4:00 P.M.	x grams
7:00 P.M.	14.4 grams

Data for a certain biology experiment are given in the table above.  If the amount of bacteria present increased by the same fraction during each of the two 3-hour periods shown, how many grams of bacteria were present at 4:00 P.M.?  



A.    12.0

B.    12.1

C.    12.2

D.    12.3

E.     12.4

Answer:  

请问two 3-hour怎么理解啊？

我直接用（10+14.4）/2=12.2  但是答案是A。。

wanghenan0431

第一个题没太明白那个12是啥用，我选9.5， 不知道对不对。
第二题的意思就是三个时间点，每段时间点增长的幅度一样，就是（X-10）/10=（14.4-X）/X， 答案是12

xrbear57

不好意思，一个题发了两遍...

xrbear57

谢谢啦~~~
第一题的答案是B~~
第二题  two 3-hour 怎么翻译呀？？

xrbear57

顶顶

尘未

第一个题看这个
http://forum.chasedream.com/GMAT_Math/thread-114363-1-1.html
第二个题
每三个小时的增长速度一样（1-4）（4-7）。按2楼解法就对啦。

xrbear57

谢谢啦～～～
要是以后ＧＷＤ里面有不会的题，就在论坛里面找就可以了吧？？

尘未

恩，搜索方法看这个，我也是今天才学的
http://forum.chasedream.com/GMAT_Preparation/thread-433635-1-1.html