maths-urgently needed(probability)

posted by .

A bag contains 5 red, 4 blue and an unknown number of m green balls.
Two balls are drawn. If probability of both being green is 1/7 find m.

  • maths-urgently needed(probability) -

    I will assume the first ball drawn is NOT returned.

    prob(2green) = (n/(9+n) * ((n-1)/(8+n)) = 1/7

    7n^2 - 7n = n^2 + 17n + 72
    6n^2 - 24n - 72 = 0
    n^2 - 4n - 12 = 0
    (n-6)(n+2) = 0
    n = 6 or n = a negative, which is no good

    there were 6 green balls

    check:
    prob(2greens) = (6/15)(5/14) = 1/7

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. 8th Grade Probability

    A box contains 6 red balls, 4 white balls, and 5 green balls. If three balls are drawn in succession without being replaced, what is the probability that they are drawn in the order red, white, green?
  2. Math

    A bag contains 5 balls,8 white balls, 9 green balls,7 blue balls& 6 yellow balls.A ball is drawn at random .Find the probablity that the ball in neither green nor red ?
  3. Basic Mathematics

    A bag contains 2 red balls, 3 blue balls and 5 green balls. 3 balls are drawn at random. Find the probability that a) the 3 balls are of different colours b) 2 balls are of the same colour c) all the 3 are of the same colour.
  4. statistics

    A jar contains 7 red balls, 5 green balls, 4 blue balls, and 3 white balls. A sample of size 7 balls is selected at random without replacement . Find t the probability that sample contains two red balls, 2 green balls, 2 blue balls, …
  5. Pre Algebra Probability

    Each of two urns contains green balls and red balls. urn 1 contains 10 green balls and 14 red balls. urn 2 contains 4 green balls and 11 red balls. if a ball is drawn from each urn what is p(red and red)?
  6. Another math related question

    Two urns both contain green balls and red balls. Urn 1 contains 6 green balls and 4 red balls and urn 2 contains 8 green balls and 7 red balls. A ball is drawn from each urn.What is the probability that both balls are red
  7. statistics /pure maths

    A box contains N identical balls of which 4 are Red, 3 are Green and the rest are White . If 3 balls are drawn at random one after the other without replacement.the probability that all 3 balls are Whit is 1/22. 1.Find the number of …
  8. Pre-Algebra

    Two urns each contain green balls and blue balls. Urn I contains 4 green balls and 6 blue balls, and Urn II contains 6 green balls and 2 blue balls. A ball is drawn at random from each urn. What is the probability that both balls are …
  9. Please Help!!! Algebra...

    Two urns each contain green balls and blue balls. Urn I contains 4 green balls and 6 blue balls, and Urn II contains 6 green balls and 2 blue balls. A ball is drawn at random from each urn. What is the probability that both balls are …
  10. Maths

    Somebody please solve this A bag contains 5 red balls 4 blue balls and m green balls.Two balls are drawn at random from the bag.If probability of both being green is 1/7,then find m.

More Similar Questions