中五的概率一問 - Ans.fyi 參考答案

中五的概率一問

2007-10-11 2:40 am

There are four number cards in a box: 2,4,5 and 9
Peter draws two cards randomly from the box. Find the probability that
(a) the product of the two numbers is odd
(b) the sum of the two numbers is less than ten
(c) the difference of the two numbers even

l want to clear step...
thx..

回答 (1)

毛毛蟲

2007-10-11 2:57 am

✔ 最佳答案

a) 1/2*1/3=1/6
First round, 2number is odd and 2 numbers is even, so is 1/2
second round, 1number is odd and 2 numbers is even so is 1/3
tIn this case, u must draw 2 odd number in 2 round respectively

b)3/4*2/3=1/2
In this case, u must not draw 9 in both rounds, so first round is 3/4, secound round is 2/3

c) in this case, u need if first round is even/odd, the second round must be the same!
So the first round is 2/4, the second round is 1/3,but u can choose odd or even, so u need *2.
the answer is
2/4*1/3*2=2/6=1/3

參考: My knowledge

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