GWD几个数学题～请教

danielleruc

Q2:

A researcher plans to identify each participant in a certainmedical experiment with a code consisting of either a single letter or a pairof distinct letters written in alphabetic order.  What is the least number of letters that can be used ifthere are 12 participants, and each participant is to receive a different code?



A.  4

B.   5

C.   6

D.  7

E.   8




选择b 5， 是怎么个解题方法啊？

Q37:

A box contains exactly 24 balls, of which 12 are red and 12are blue.  If two balls are to bepicked from this box at random and without replacement, what is the probabilitythat both balls will be red?

答案是11／46，怎么算出来呢？ 我是c12 2/c 24 2,想从12个红的里面拿2个的概率 除去 24个随机抽2个的概率，可是算出来不对。。。谢谢

zhangfei3322

Q2: N+ C(N,2),从比较小的数开始试，4的时候是8不够，5的时候15够了,注意是in alphabetic order

Q37：C(12,2)/C(24,2)