Results 1 to 6 of 6

Math Help - red and black cubes

  1. #1
    Newbie
    Joined
    Apr 2010
    Posts
    11

    red and black cubes

    I've got a maths exam next week and i need to know how to work this question out for my revision so please could u show me:

    There are some cubes in a bag. The cubes are eithert red (R) or black (B).
    The teacher says:
    If you take a cube at random out of the bag, the probability that it will be red is 1/5.
    (a) what is the probabilty that the cube will be black?

    (b) A pupil takes one cube out of the bag. It is red. What is the smallest number of black cubes there could be in the bag?

    (c) Then the pupil takes another cube out of the bag. It is also red. From this new information, what is the smallest number of black cubes there could be in the bag?

    (d) A different bag has blue (B), green (G) and Yellow (Y) cubes in it. There is at least one of each of the three colours.
    The teacher says:
    If you take a cube at random out of the bag, the probability that it will be green is 3/5.
    There are 20 cubes in the bag. What is the greatest number of yellow cubes there could be in the bag?

    Please can you show your working for all of the questions so i understand it.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member Anonymous1's Avatar
    Joined
    Nov 2009
    From
    Big Red, NY
    Posts
    517
    Thanks
    1
    Quote Originally Posted by molly View Post
    I've got a maths exam next week and i need to know how to work this question out for my revision so please could u show me:

    There are some cubes in a bag. The cubes are eithert red (R) or black (B).
    The teacher says:
    If you take a cube at random out of the bag, the probability that it will be red is 1/5.
    (a) what is the probabilty that the cube will be black?

    \color{red}{P(\text{black}) = 1 - 1/5 = 4/5}

    (b) A pupil takes one cube out of the bag. It is red. What is the smallest number of black cubes there could be in the bag?

    \color{red}{4. \text{ See above.}}

    (c) Then the pupil takes another cube out of the bag. It is also red. From this new information, what is the smallest number of black cubes there could be in the bag?

    \color{red}{\text{Smallest now is... Red 2/10 so Black is 8/10. The answer is 8.}}

    (d) A different bag has blue (B), green (G) and Yellow (Y) cubes in it. There is at least one of each of the three colours.
    The teacher says:
    If you take a cube at random out of the bag, the probability that it will be green is 3/5.
    There are 20 cubes in the bag. What is the greatest number of yellow cubes there could be in the bag?

    \color{red}{(3/5)\times(20).}

    Please can you show your working for all of the questions so i understand it.
    aNon1
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Apr 2010
    Posts
    11
    Quote Originally Posted by Anonymous1 View Post
    aNon1
    wats aNon1?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member Anonymous1's Avatar
    Joined
    Nov 2009
    From
    Big Red, NY
    Posts
    517
    Thanks
    1
    Quote Originally Posted by molly View Post
    wats aNon1?
    My name, ofcourse.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Apr 2010
    Posts
    11
    On question (c) where did u get the /10 bit from?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member Anonymous1's Avatar
    Joined
    Nov 2009
    From
    Big Red, NY
    Posts
    517
    Thanks
    1
    Quote Originally Posted by molly View Post
    On question (c) where did u get the /10 bit from?
    We know the probability is 1/5...

    We know there are at least 2...

    2/10=1/5
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Probabilty black jack
    Posted in the Statistics Forum
    Replies: 2
    Last Post: October 17th 2011, 08:42 PM
  2. Formula for Black Scholes
    Posted in the Advanced Applied Math Forum
    Replies: 0
    Last Post: March 3rd 2010, 03:46 AM
  3. Black-scholes equation
    Posted in the Advanced Applied Math Forum
    Replies: 0
    Last Post: March 2nd 2010, 03:53 AM
  4. Application of Black-Scholes
    Posted in the Business Math Forum
    Replies: 0
    Last Post: November 23rd 2009, 08:57 AM
  5. Red and Black balls in urn
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: September 20th 2009, 03:28 AM

Search Tags


/mathhelpforum @mathhelpforum