probability

A)
As there are 4 person in room A
the required probability
=P(the patient is not chosen in the first time)
= 3/4

B)
the required probability
=P(the patient is chosen in the first time but not in the second)
= 1/4 (4/5)
= 1/5

C)
the required probability
=P(the patient is chosen in the first and second time but not in the third one)
= 1/4 (1/5) (3/4)
= 3/80

D)
the required probability
=P(a nurse is chosen in the first and second time{may not the same one})+
P(a non-nurse is chosen in the first time but a nurse is chosen in the second )
= 2/4 (3/5) + 2/4 (2/5)
= 6/20 + 4/20
= 24/400
= 3/50

2007-10-14 13:25:00 補充：
sorry part C) and D) is wrong as I mislead the question and wrong calculationthe answer should be :C)the required probability=P(the patient is chosen in the first and second time)= 1/4 (1/5)= 1/20D)the required probability= 2/4 (3/5) 2/4 (2/5)= 1/2

2007-10-14 13:26:12 補充：
D)the required probability=P(a nurse is chosen in the first and second time{may not the same one}) P(a non-nurse is chosen in the first time but a nurse is chosen in the second )= 2/4 (3/5) 2/4 (2/5)= 6/20 4/20= 10/20= 1/2

2007-10-14 13:27:37 補充：
補充時因看不到分數下面重打：D)the required probability=P(a nurse is chosen in the first and second time{may not the same one}) P(a non-nurse is chosen in the first time but a nurse is chosen in the second )= 2/4 (3/5) ＋ 2/4 (2/5)= 6/20 ＋ 4/20= 10/20= 1/2

A)

As there are 4 person in room A

the required probability

=P(the patient is not chosen in the first time)

= 3/4



B)

the required probability

=P(the patient is chosen in the first time but not in the second)

= 1/4 (4/5)

= 1/5



C)

the required probability

=P(the patient is chosen in the first and second time)

= 1/4 (1/5)

= 1/20


D)

the required probability

=P(a nurse is chosen in the first and second time{may not the same one})

P(a non-nurse is chosen in the first time but a nurse is chosen in the second )

= 2/4 (3/5) ＋ 2/4 (2/5)

= 6/20 ＋ 4/20

= 10/20

= 1/2

(a)
P(not choose patient from room A)=3/4

(b)
P(choose patient from room A & not choose patient from room B)
=(1/4) * (4/5)
=1/5

(c)
P(choose patient from room A & choose nurse from room B)
=(1/4)*(1/5)
=1/20

(d)
P(choose patient from room A & choose nurse from room B)+P(not choose nurse from room A & choose nurse from room B)
=(2/4)*(3/5)+(2/4)*(2/5)
=3/10+1/5
=1/2

2007-10-14 13:21:53 補充：
(c)should beP(choose patient from room A & choose patient from room B)=(1/4)*(1/5)=1/20

2007-10-14 13:25:21 補充：
1,2樓就唔講la...3樓o個位...(c) : 題目冇寫佢會係room c再揀人走....所以唔使乘第三個.....(d) : 同我一樣....不過你分數相加竟然錯左....

in a hospital,there are 3 rooms on a floor

in room A, there are 1 doctor,2 nurses and 1 patient

in room B, there are 2 doctor and 2 nurses

in room C, there are 3 nurses

a person is chosen from room A and he enters room B. then, a person is chosen from room B and he enters room C . find the probability that

(a) the patient is still in room A

(b) the patient is in room B

(c) the patient is in room C

(d) all people in room C are nurses


a. 1/3
b. 1/2
c. 1/2
d. 1/3

a. 1/3
b. 1/2
c. 1/2
d. 1/3