GWD1-Q31

notidgen

Q37:

A jar contains 16 marbles, of which 4 are red, 3 are blue, and the rest are yellow.  If 2 marbles are to be selected at random from the jar, one at a time without being replaced, what is the probability that the first marble selected will be red and the second marble selected will be blue?

 

A.      3/64

B.       1/20

C.      1/16

D.      1/12

E.       1/8

答案是b，4/16*3/15*1，这样算对么？请nn指教，谢拉^_^

notidgen

up，没有人理我。。。

wxy831

注意one at a time without being replaced，就是拿走之后不放回，一开始取红球，4/16,第二次取总数已经少一个了，所以3/15,两者乘下