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Math Help - I need someone to explain the workout of this question please

  1. #1
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    I need someone to explain the workout of this question please

    Question A jar contains 10 red marbles and 30 green ones. How many red marbles must be added to the jar so that 60% of the marbles will be red?

    Answer Assuming the required number of red marbles to be=x

    40+x marbles are in the jar, of which 10+x are red. Since we want the fraction of red marbles to be 60%, we have:

    10+x = 60% = 3/5
    40+x

    Cross multiplying we get:

    50+5x=120+3x => 2x=70 => x=35


    I am having problem understanding why the question is done this way? As in, I dont understand why 10+x is divided by 40+x ??? Is there a formula applied in it? If so i'm not aware of it, im not familiar with the formula, please explain.

    And if not i cant understand the logic of how/why is it worked out this way? Is there any other way of doing it? Some simple to understand, straight forward way?
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  2. #2
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    Quote Originally Posted by Bish4n View Post
    Question A jar contains 10 red marbles and 30 green ones. How many red marbles must be added to the jar so that 60% of the marbles will be red?

    Answer Assuming the required number of red marbles to be=x

    40+x marbles are in the jar, of which 10+x are red. Since we want the fraction of red marbles to be 60%, we have:

    10+x = 60% = 3/5
    40+x

    Cross multiplying we get:

    50+5x=120+3x => 2x=70 => x=35


    I am having problem understanding why the question is done this way? As in, I dont understand why 10+x is divided by 40+x ??? Is there a formula applied in it? If so i'm not aware of it, im not familiar with the formula, please explain.

    And if not i cant understand the logic of how/why is it worked out this way? Is there any other way of doing it? Some simple to understand, straight forward way?
    because x = number of red marbles added.

    Now x+10= new number of red marbles in the jar

    x+40= x+10+30= new total number of marbles in the jar after adding x red marbles.

    now, \frac {x+10}{x+40}=ratio of red marbles to the total marbles.
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  3. #3
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    percentage

    posted by Bish4n

    The simple solution. 30 green marbles equals 40 percent of the new total.new total is 75 ( 30 divided by .40) new total minus old equals reds added (35)


    bj
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by Bish4n View Post
    that was the best answer - honest!
    Quote what you are refering to so we know what you are talking about

    RonL
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  5. #5
    Grand Panjandrum
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    Quote Originally Posted by Bish4n View Post
    that was the best answer - honest!
    If you are refering to bjhopper's post it is an explanation of why that is the solution but unless you want to guess and check does not help you find the solution which the earlier post did do.

    RonL
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