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# impossible probablity question watch

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1. for a i'm getting 18/35 but the book says 7/10
2. See my message earlier.
3. saw it but sorry thats wrong
4. 7/10!? that cant be right

Are you sure that 2/3 of the passes are white is correct?!
5. (Original post by dizzy 200)
for a i'm getting 18/35 but the book says 7/10
It can't be 7/10 because if you add together 7/10 + 2/3 you get 1 and 11/30 which isn't correct...

Have you typed out the whole question?
6. question states that 6/10 of all the passes have clips.2/3 of the white passes have clips and 4/7 of the yellow have clips

therfore yellow pass would be 6/10*4/7 (clip and yellow )+ 4/10*3/7 (chain and yellow)= 18/35

typed out question as it was in the book
7. (Original post by dizzy 200)
question states that 6/10 of all the passes have clips.2/3 of the white passes have clips and 4/7 of the yellow have clips

therfore yellow pass would be 6/10*4/7 (clip and yellow )+ 4/10*3/7 (chain and yellow)= 18/35

typed out question as it was in the book
I'm sure the first post said 2/3 of passes are white...
8. it says that2/3 of the white passes have clips
9. I think that my asnwer is right.
10. i think my answer is right too but the book says it's wrong
11. (Original post by dizzy 200)
i think my answer is right too but the book says it's wrong
Sometimes the books make mistakes.....like gcse bitesize revision guide....i was sure i was right on the circle theorems questions, and i asked all my friends and they agreed, but the answer in the book was really strange and unorthodox!!!!
It was the book that was wrong - i asked teacher.
12. Right for a)

firstly work out what 2/3 of 6/10 is which is 2/5, so the probability that a pass is white with a clip is 2/5, which means that the probability of a pass being yellow with a clip is 2/10 (because 6/10 - 4/10 = 2/10)

We know that 4/7 of the yellow passes have clips so 3/7 of yellow passes will have a chain, so then if we divide 2/10 by 4 (to get what one seventh is) and then multiply this by 3 we get the probability of a pass being yellow with a chain which gives 1/20 X 3 = 3/20, then if you add this to 2/10 you get 7/20

Hmmmmm not sure if this is correct though as it's different to the answer in your book plus I've probably mucked up some where and/or have a dodgey way of thinking...
13. wow think you're making it too complicated ! are you doing s1?
14. (Original post by dizzy 200)
wow think you're making it too complicated ! are you doing s1?
nope, I'm doing my GCSE's
15. (Original post by dizzy 200)
i've been trying to do this questions for ages can anyone help?
Security passes for a company are either yellow or white and are provided with a clip to go on your pocket or a chain to be worn around the neck. The probability that a pass has a clip is 6/10 and 2/3 of the white passes and 4/7 of the yellow are fitted with clips. A member of the company is stopped. Find the probability that the
a) pass is yellow
b) the pass is yellow with a chain
if two people are stopped at random as they enter the company
C) find the probability that one pass will be yellow,and the other white and one will have a clip and the other a chain
You have changed the question! I'll work out this new one.

(a) When w = number of white, and y= number of yellow,
(2/3)w + (4/7)y = (6/10)(w+y)
(2/3)w + (4/7)y = (6/10)w + (6/10)y
Eliminate fractions:
14w = 6y
p(yellow) = y/(y+w) = (7/3w) / (7/3w + w)
(7/3w) / (7/3 + 1)w = (7/3)/(10/3) = 7/10

(b) - In a minute.
16. (a) 7/10
17. (b) 7/10 x 3/7 = 21/70 = 3/10
18. Very good, dint think of that myself, the mis-typed fake question was so much easier, cant u just mis-type it again!
19. (Original post by YorkshirePhoeni)
Very good, dint think of that myself, the mis-typed fake question was so much easier, cant u just mis-type it again!
Who is that to?

And what are the other aswers from the book please?
20. (c) P(white clip) x p(yellow chain)

= (3/10 x 2/3) x (7/10 x 3/7)

= 7/15 x 9/70 = 3/50

P(yellow clip) x p(white chain)

= (7/10 x 4/7) x (3/10 x 1/3)

= 7/30 x 6/35 = 1/25

Two added together = 5/50 = 1/10

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