probability?

nam

2007-06-02 6:02 pm

Isabella has 2blue,2grey and 3yellow umbrellas at home .She also keeps another blue umbrella in her office .On a rainy day, she pick an umbrella at random from her home and goes to work.When she leaves the office and returns home ,she again picks an umbrella at random from her office .Find the probability that she now has

(a)1grey umbrella at home,
(b)1blue umbrella in her office,
(c)no blue umbrellas in her office.

answers:(a)1/7 (b)9/14 (c)5/14 pls.

回答 (1)

wing hang

2007-06-02 6:18 pm

✔ 最佳答案

(a)
P(1 grey umbrella in home)=P(1 grey umbrella in home to office)xP(one blue umbrella return to home)=(2/7)x(1/2)=1/7
(b)
P(1 blue umbrella in her office)=P(1 blue umbrella to office from home)+P(1 grey umbrella to office→1blue umbrella to home from office)+P(1 yellow umbrella to office from home→1blue umbrella to home from office)
=(2/7)+(2/7)x(1/2)+(3/7)x(1/2)=9/14
(c)P(1 blue umbrella in her office)+P(no blue umbrellas in her office)=1
P(no blue umbrellas in her office)=1-9/14=5/14

👍 0 👎 0