Probability

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A bag contains some balls of which 1/4 are red. Forty more balls of which 5 are red are added. If 1/5 of all the balls are red, how many balls was there originary?

  • Probability -

    original number of balls --- x
    original number of red balls = x/4

    number of red balls added = 5
    total balls added = 45

    new total = x+45
    new red ball total = (x/4 + 5)

    (1/5)(x + 45) = x/4 + 5
    x/5 + 9 = x/4 + 5
    times 20
    4x + 180 = 5x + 100
    x = 80

    you had 80 balls

    check:
    you had 80 of which 20 were red
    you added 45 of which 5 were red
    new total 125
    new number of red = 25

    is 25 equal to 1/5 of 125 ? YES!!

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