Stuck on a Probability Question
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Guest_25 Nov
Stuck on a Probability Question
Hi
Can anyone help to explain the workings to the answer to the following probability question.
There are 12 boys and 8 girls in a class, including a brother and a sister. If one boy and one girl are chosen at random from the boys and girls respectively, what is the probability that the brother and sister are both chosen?
Ans = 1/190
Can anyone help to explain the workings to the answer to the following probability question.
There are 12 boys and 8 girls in a class, including a brother and a sister. If one boy and one girl are chosen at random from the boys and girls respectively, what is the probability that the brother and sister are both chosen?
Ans = 1/190
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Guest_25 Nov
Amended question
Sorry, I posted the wrong question. It is re-presented below, can anyone show how to arrive at the answer:
There are 12 boys ans 8 girls in a class, including a brother and sister. If 2 pupils are chosen at random from the class, what is the probability that the brother and sister are both chosen?
Ans = 1/190
There are 12 boys ans 8 girls in a class, including a brother and sister. If 2 pupils are chosen at random from the class, what is the probability that the brother and sister are both chosen?
Ans = 1/190
Lets call the Brother Child A and the sister Child B.
The chance of selecting A from the class is 1/20 and the chance of selecting B from the remainer is 1/19. So the chance of selecting A followed by B is 1/20 x 1/19 = 1/390.
But you have to consider the other alternative valid option which is selecting B first followed by A which is also 1/390.
Therefore the chance of selecting AB or BA is therefore 2/390 = 1 in 190.
The chance of selecting A from the class is 1/20 and the chance of selecting B from the remainer is 1/19. So the chance of selecting A followed by B is 1/20 x 1/19 = 1/390.
But you have to consider the other alternative valid option which is selecting B first followed by A which is also 1/390.
Therefore the chance of selecting AB or BA is therefore 2/390 = 1 in 190.
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Guset_25 Nov
One last probaility question
Hi KenR.
If you can help on this last probability question, it would be much appreciated. I will also include my (incorrect) workings so far.
In a drawer are 3 black socks and 2 white socks. If 2 are picked at random, what is the probability that they will be the same colour?
Ans = 2/5
My workings:
Let Black = B, and White = W
Probability of getting one black, B = 1/5
Probability of getting one white from the remainder, C= 1/4
Therefore
Probability of getting 2 black socks = 2 times 1/5 = 2/5
Probability of getting 2 white socks socks = 2 times 2/4 =1/2
Therefore probaility of getting either 2 white socks or 2 blacks socks is:
2/5 times 1/2 = 2/10 = 1/5 = incorrect answer
Can you please help?
If you can help on this last probability question, it would be much appreciated. I will also include my (incorrect) workings so far.
In a drawer are 3 black socks and 2 white socks. If 2 are picked at random, what is the probability that they will be the same colour?
Ans = 2/5
My workings:
Let Black = B, and White = W
Probability of getting one black, B = 1/5
Probability of getting one white from the remainder, C= 1/4
Therefore
Probability of getting 2 black socks = 2 times 1/5 = 2/5
Probability of getting 2 white socks socks = 2 times 2/4 =1/2
Therefore probaility of getting either 2 white socks or 2 blacks socks is:
2/5 times 1/2 = 2/10 = 1/5 = incorrect answer
Can you please help?
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Guest
Probability
Guest 55,
You have literally just beaten me to it. I was about to submit the very same solution.
C
You have literally just beaten me to it. I was about to submit the very same solution.
C
