请教XDF(绿皮教程)－PS－230/196/462/568

小姜

196. Each of the integers from 0 to 9,  inclusive,  is written on a seperate slip of blank paper and the ten slips are dropped into a hat. if the slips are then drawn on at a time without replacement, how many must be drawn to ensure that the numbers on two of the slips drawn will have a sum of 10?

A. three    B. Four   C. Five   D. six  E. Seven (E)

230. of the science books in a certain supply room,50 are botany, 65 are zoology, 90 are on physics, 50 are geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed are on the same science.

A. 81  B. 159  C.166  D.285  E. 324  (E)

这两道题都是问在一堆组合里面去出至少要取出多少个元素才能使这些取出的元素中有符合某些条件的元素。请教这样的题使什么思路呢

462. A 2-year certificate of deposit is purchased for k dollars . If the certificate earns intrest at an annual rate of 6 percent compounded quarterly, which of the following represents the value, in dollars, of the certificate at the end of the 2 years?!

A. (1.06)^2k

B.  (1.06)^8k

C. (1.015)^2k

D. (1.015)^8k

E. (1.03)^4k

D

at an annual rate of 6 percent compounded quarterly  什么意思啊？！

568. What is the least number of digits (including repetitions) needed to express 10^100 in decimal notation?

A. 4  B. 100 C.101  D.1,000 E 1,001  C

这道题的题干是什么意思呢？！

 请大家指教啊！

 

hitlzc

568. What is the least number of digits (including repetitions) needed to express 10^100 in decimal notation?
A. 4  B. 100 C.101  D.1,000 E 1,001  C
这道题的题干是什么意思呢？！

就是以十进制表达有多少位了。

好比10^3表达成十进制就是4位数了。

10^100是101位数。

hitlzc

462. A 2-year certificate of deposit is purchased for k dollars . If the certificate earns intrest at an annual rate of 6 percent compounded quarterly, which of the following represents the value, in dollars, of the certificate at the end of the 2 years?!
A. (1.06)^2k
B.  (1.06)^8k
C. (1.015)^2k
D. (1.015)^8k
E. (1.03)^4k
D
at an annual rate of 6 percent compounded quarterly  什么意思啊？！

就是年利率是6%,按季度计算复利。

所以季度利率是1.5%,二年计4*2=8次复利

hitlzc

230. of the science books in a certain supply room,50 are botany, 65 are zoology, 90 are on physics, 50 are geology, and 110 are on chemistry. If science books are removed randomly from the supply room, how many must be removed are on the same science.
A. 81  B. 159  C.166  D.285  E. 324  (E)

http://forum.chasedream.com/dispbbs.asp?BoardID=22&replyID=1670173&id=176604&skin=0

hitlzc

196. Each of the integers from 0 to 9,  inclusive,  is written on a seperate slip of blank paper and the ten slips are dropped into a hat. if the slips are then drawn on at a time without replacement, how many must be drawn to ensure that the numbers on two of the slips drawn will have a sum of 10?
A. three    B. Four   C. Five   D. six  E. Seven (E)

两个数能形成10的有(1,9)(2,8)(3,7)(4,6)

所以只有0和5不能与其他数形成10。

而保证一定有一对数形成10：

当取出数为0，5，以及四对数中每对数取一个后，再取任何一个都必然形成一对数为10。

所以要拿7个数。

BTW：这本书的题好象很少看到有同学问，好象同费费有重复的地方。XDF不讲解吗？

小姜

天气这么热辛苦拉！

多谢帮助！