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Bunuel
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What is OA? M confused.

Stay Hungry Stay Foolish
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Aekagra
What is OA? M confused.

Stay Hungry Stay Foolish

Hi

OA will be revealed on 6th Feb as the question says. Though if you go through the 2 solutions posted above you could see that they have explained the answer to be A.

Whats the confusion about may I know?
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2) The probability that one boy and one girl will be chosen is 16/33..
Whatever Ans we get can be of boys or girls..
So insufficient..
(12-g)/12 *g/11* 2=16/33....... (12-g)g=32...

How do we get this 2 in the left side of equation?
Thank you!
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chetan2u
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From a class of 12 students, two students will be randomly chosen simultaneously. If g is the number of girls in the class, what is the value of g?

(1) The probability that two girls will be chosen together is 1/11.
(2) The probability that one boy and one girl will be chosen is 16/33.


Let the number of girl be g, then the number of boys =12-g...

(1) The probability that two girls will be chosen together is 1/11.
P of first as girl = g/12..
P of second as girl = (g-1)/11..
Combined prob = g/12 * (g-1)/11=1/11...
g (g-1)=12=4*3...
So g is 4
Sufficient..
2) The probability that one boy and one girl will be chosen is 16/33..
Whatever Ans we get can be of boys or girls..
So insufficient..
(12-g)/12 *g/11 * 2=16/33....... (12-g)g=32...
So g can be 8 or 4..
Insuff

A

Hi, thanks for the answer.
I still don't understand though where you got the 2 from in statement 2 :
(12-g)/12 *g/11 * 2=16/33....... (12-g)g=32...

Many thanks in advance for your answer
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tahina
chetan2u
Bunuel
From a class of 12 students, two students will be randomly chosen simultaneously. If g is the number of girls in the class, what is the value of g?

(1) The probability that two girls will be chosen together is 1/11.
(2) The probability that one boy and one girl will be chosen is 16/33.


Let the number of girl be g, then the number of boys =12-g...

(1) The probability that two girls will be chosen together is 1/11.
P of first as girl = g/12..
P of second as girl = (g-1)/11..
Combined prob = g/12 * (g-1)/11=1/11...
g (g-1)=12=4*3...
So g is 4
Sufficient..
2) The probability that one boy and one girl will be chosen is 16/33..
Whatever Ans we get can be of boys or girls..
So insufficient..
(12-g)/12 *g/11 * 2=16/33....... (12-g)g=32...
So g can be 8 or 4..
Insuff

A

Hi, thanks for the answer.
I still don't understand though where you got the 2 from in statement 2 :
(12-g)/12 *g/11 * 2=16/33....... (12-g)g=32...

Many thanks in advance for your answer

Hi

I think the '2' here is because there could be two cases: Either first student chosen is a boy, second one is a girl OR first student chosen is a girl, second one is a boy.

And for each of these two cases, Probability will be the same = [(12-g)*g] / [12*11].
So rather than add the two cases, he has multiplied by '2'.
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I think this way for multiplication of 2 for st.2.

Ways of selecting of a boy. 12-gC1= 12-g
Ways of selecting of a girl gC1 = g
Ways of selecting 2 from 12 students = 12C2

Then he probability of selecting one boy and one girl is = (12-g)*g/(12*11/2)= 16/33

Now we will get multiplication of 2 as shown in your explanation.

YDW I still have a doubt. Why we could not solve it as below.
(12-g)/12 * g/11= 16/33
I have solved many such questions and got the correct answer. Probably, the given answer choice was wrong.
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