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# Stuck on question (Probability or possible quadratic equation) Watch

1. Hi .

Not sure how to do this question. It mentioned probability but am I to just solve it like a quadratic equation?

Thanks
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2. (Original post by jojo55)
Hi .

Not sure how to do this question. It mentioned probability but am I to just solve it like a quadratic equation?

Thanks
No. Draw a tree diagram. What is the probability that Joshua takes one white sock and one black sock in terms of y?

Equate this expression to 6/11 and simplify/re-arrange to get the given quadratic equation. They do not want you to solve it just yet, they want you to use the facts given to get that quadratic.
3. (Original post by Zacken)
No. Draw a tree diagram. What is the probability that Joshua takes one white sock and one black sock in terms of y?

Equate this expression to 6/11 and simplify/re-arrange to get the given quadratic equation. They do not want you to solve it just yet, they want you to use the facts given to get that quadratic.

I get to show the probability of a white sock out of the total amount of socks of y + 5

Plus, I get to show the probability of a black sock.

Is the next bit:

()() =

Not 100% on that as the mark scheme says it is 2()() = instead.
4. (Original post by jojo55)
I get to show the probability of a white sock out of the total amount of socks of y + 5

Plus, I get to show the probability of a black sock.

Is the next bit:

()() =

Not 100% on that as the mark scheme says it is 2()() = instead.
You've done:

P(white sock) * P(black sock).

What about the other possibility of:

P(black sock) * P(white sock)?

You need to add those together:

P(white sock)*P(black sock) + P(black sock)*P(white sock) =

Did you draw a tree diagram? If so, it should have been obvious of the two different routes you can go to get the requires probability.
5. (Original post by jojo55)
Hi .

Not sure how to do this question. It mentioned probability but am I to just solve it like a quadratic equation?

Thanks
took me a while but i think i got it lol:

2(y/y+5 x 5/y+4) = 6/11

2(5y/y2 + 9y + 20) = 6/11

10y/y2 + 9y + 20 = 6/11

110y/y2 + 9y + 20 = 6

110y = 6y2 + 54y + 120

0= 6y2 - 56y + 120

0= 3y2 -28y +60
6. (Original post by qwerty0301)
took me a while but i think i got it lol:
Full solutions are against forum guidelines, have you read the posting guide?

Thanks.
7. (Original post by Zacken)
Full solutions are against forum guidelines, have you read the posting guide?

Thanks.
(Original post by qwerty0301)
took me a while but i think i got it lol:

2(y/y+5 x 5/y+4) = 6/11

2(5y/y2 + 9y + 20) = 6/11

10y/y2 + 9y + 20 = 6/11

110y/y2 + 9y + 20 = 6

110y = 6y2 + 54y + 120

0= 6y2 - 56y + 120

0= 3y2 -28y +60

Thanks for the help.

I got the same solution after I figured out that that it wasn't both over y+5, that I put in my earlier post.

Thanks again.

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