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    A box contains yellow, blue and green pencils in the ratio 3:2:5
    There is nothing else in the box

    6 Yellow pencils are added to the box
    One pencil is picked at random from the box

    The probability of it being yellow is 3/8
    Show that the probability of it being blue is 5/28.
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    What have you tried?
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    (Original post by old_engineer)
    What have you tried?
    I turned the ratio 3:2:5 into fractions so,

    Yellow = 3/10
    Blue = 2/10
    Green = 5/10

    I then found the difference between 3/10 (fraction before) and 3/8 (probability after) which is 3/40 and 6 yellows were added therefore 3/40 = 6 pencils.
    So 2 pencils = 1/40 and there are 80 pencils in the box after the 6 were added.

    Before the 6 were added there must have been 74 pencils and 2/10 pencils were blue. I multiplied 74 by 2/10 and got a decimal so i must have done something wrong but I'm not sure what.
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    The ratio is: 3x:2x:5x
    We know 6 yellow pencils have been added to the box therefore our new ratio is 3x 6:2x:5x.
    Now what is the p(y) in terms of x? Set this equal to 3/8 (since that is the p(y) in numbers we can understand. Solve for x. Now do the same for blue and sub your x value in.

    Edit: I didn’t mean to attach the image, I tried to spoiler it but it didn’t work for some reason and it won’t let me delete it. Sorry
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    (Original post by Y11_Maths)
    The ratio is: 3x:2x:5x
    We know 6 yellow pencils have been added to the box therefore our new ratio is 3x 6:2x:5x.
    Now what is the p(y) in terms of x? Set this equal to 3/8 (since that is the p(y) in numbers we can understand. Solve for x. Now do the same for blue and sub your x value in.

    Edit: I didn’t mean to attach the image, I tried to spoiler it but it didn’t work for some reason and it won’t let me delete it. Sorry
    No worries, thanks anyway
 
 
 
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Updated: March 11, 2018

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