有關probabilities

yen san

2010-05-06 3:31 am

1. in the throwing two dice, find the probability of getting
(a) 2 even numbers
(b) 1 even number and 1 odd numbers

2. The probability that a man will be alive in 25 years is 0.8, and the probability
that his wife will be alive in 25 years is 0..85. Find the probability that
(a) both will be alive in 25 years
(b) only the man will be alive in 25 years
(c) at least one will be alive in 25 years

回答 (1)

用戶2053

2010-05-06 3:48 am

✔ 最佳答案

1a)
P(2 even numbers)
= P(1st dice even) x P(2nd dice even)
= 3/6 x 3/6
= 1/4
b)
P(1 even number and 1 odd numbers)
= P(1st dice even , 2nd dice odd) + P(1st dice odd , 2nd dice even)
= 3/6 * 3/6 + 3/6 * 3/6
= 1/2
2a)
P(both will be alive in 25 years)
= 0.8 * 0.85 = 0.68
b)
P(only the man will be alive in 25 years)
= P(the man will be alivei n 25 years and the wife not alive in 25 years)
= 0.8 * (1 - 0.85)
= 0.12
c)
P(at least one will be alive in 25 years)
= 1 - P(all of them not alive in 25 years)
= 1 - (1 - 0.8)(1 - 0.85)
= 0.97

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