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# F4 Maths

Probabilities

謝謝..1.

Bag A contains 7 red balls, and 5 blue balls. Bag B contains 5 red balls

and 4 green balls. One ball is randomly drawn from A into Bag B. Then

one ball is drawn from Bag B randomly and put into A. Final, a ball is drawn

from A at random. Find the probability that the final ball drawn from bag A is(a) blue

(b) red-----2.

There are 2 white, 4 green and 5 red balls in a bag. Two balls are drawn at

random with replacement. What is the probability that(a) both are red ?

(b) both are of the same colour

(c) they are different in colour-----3.

The probability that a man will be alive in 25 years is 0.8,and the probability

that hin 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

詳細解答,列式 ..

謝謝..

### 1 Answer

- 9 years agoFavorite Answer
1. (b) (a)

P(Red) = P(RRR) + P(RBR) + P(BRR) + (BBR)

= 7/12 x 6/10 x 7/12 + 7/12 x 4/10 x 6/12 +

5/12 x 5/10 x 8/12 + 5/12 x 5/10 x 7/12

=93/160

P(Blue) = 1 - 93/160 = 67/160

2.

a) 5/11 x 4/10 =2/11

b) P(WW) +P(GG) + P(RR)

= 2/11 x 1/10 + 4/11 x 3/10 + 2/11

= 17/55

c) P(different in color) = 1 - P(same in color)

= 1 - 17/55

= 38/55

3.

a) 0.8 x 0.85 = 0.68

b) 0.8 x (1 - 0.85) = 0.12

c) P(at least one be alive) = 1 - P(both die)

= 1 - (1 - 0.8) x (1 - 0.85)

= 0.97

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