Help needed for Probability qustion please

Hi,
I am struggling on a question and any help given would be much appreciated. Here it is:
A class consists of seven boys and nine girls two different members of the class are chosen at random. A is the event that {the first person is a girl} and B is the event that {the second person is a girl}. Find the probability of of B given A' (B/A')
Thanks Jack

Reply 1

J.F.N

1

Jack

Hi,
I am struggling on a question and any help given would be much appreciated. Here it is:
A class consists of seven boys and nine girls two different members of the class are chosen at random. A is the event that {the first person is a girl} and B is the event that {the second person is a girl}. Find the probability of of B given A' (B/A')
Thanks Jack

A' is the complement of A--i.e. A' is the event that the first person is a boy, so that P(A')=7/16.
P(B|A')=P(B n A')/P(A')=P(B and A')/P(A')=P(second person girl AND first person boy)/P(A')=(7/16).(9/15)/(7/16)=9/15

Reply 2

Jack

OP

Much appreciated but unfortunately the answer according to a textbook i have is 3/5. Altough it is encouraging that both you and i both achieved the exact same result. Good try but try again - lol,
Thanks Jack

Reply 3

J.F.N

1

Jack

Much appreciated but unfortunately the answer according to a textbook i have is 3/5. Altough it is encouraging that both you and i both achieved the exact same result. Good try but try again - lol,
Thanks Jack

The textbook is wrong.

Reply 4

~Bex~

14

Hello people, are you awake?!

9/15 = 3/5!!

Reply 5

Speleo

7

9/15 = 3/5
Or am I missing something?

EDIT: Beaten O: .

Reply 6

J.F.N

1

Ha! The prodigal mathematician.

Reply 7

~Bex~

14

Excuse me? Is this supposed to be a sarcastic comment aimed at me/speleo? If it is, then may I remind you that YOU are the one who was unable to see that 9/15=3/5

Reply 8

J.F.N

1

~Bex~

Excuse me? Is this supposed to be a sarcastic comment aimed at me/speleo? If it is, then may I remind you that YOU are the one who was unable to see that 9/15=3/5

The prodigal mathematician was intended to be self-deprecating.

Reply 9

Jonny W

8

prodigal $\neq$ prodigious

Reply 10

J.F.N

1

Jonny W

prodigal $\neq$ prodigious

I know. Prodigal=reckless.

Reply 11

Chewwy

17

~Bex~

Excuse me? Is this supposed to be a sarcastic comment aimed at me/speleo? If it is, then may I remind you that YOU are the one who was unable to see that 9/15=3/5

lol

Help needed for Probability qustion please

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