Ask Me Help Desk

Ask Me Help Desk (https://www.askmehelpdesk.com/forum.php)
-   Math & Sciences (https://www.askmehelpdesk.com/forumdisplay.php?f=402)
-   -   AQA probability maths gcse (https://www.askmehelpdesk.com/showthread.php?t=316447)

  • Feb 12, 2009, 02:55 AM
    alirosie
    AQA probability maths gcse
    I should start by saying I am a mature student (embarrassed! ) and it isn't strictly speaking homework but I am using the AQA website to work through past papers as I am self taught. I am struggling with a probability question and I find that using probability trees helps me. Well, the question is:
    You have 100 people divided into 14 male managers and 26 male teachers, 8 female managers and 52 female teachers. What is the probability that you will select a male teacher and any female.

    On my "tree" I have put the probability of males / females is 2/5 and 3/5 respectively.
    I have then on my branch off the "males" I have divided males into 7/20 probability for manager and 13/20 probability for teacher. On my branch off the "females" I have divided females into 2/15 managers and 13/15 teachers.

    I worked out then that probability of male teacher = 2/5 x 13/20 and any female = 3/5 x 2/15 plus 3/5 x 13/15

    Needless to say my answer is wrong (AQA provide mark sheets). Help! :(
  • Feb 12, 2009, 04:53 AM
    alirosie
    OK - so I did it again - the question asks for the answer in tree form so: I re-did it as male teachers = 26/100 (13/50) multiplied by "any female" = 60/99 (20/33) = 260/1650 or 26/165

    They give the answer as the above but multiplied by 2. Where does the 2 come from. Please help because I'm tearing my hair out.:o
  • Feb 12, 2009, 05:25 AM
    alirosie
    Quote:

    Originally Posted by alirosie View Post
    OK - so I did it again - the question asks for the answer in tree form so: I re-did it as male teachers = 26/100 (13/50) multiplied by "any female" = 60/99 (20/33) = 260/1650 or 26/165

    They give the answer as the above but multiplied by 2. Where does the 2 come from. Please help because I'm tearing my hair out.:o


    Sorry - been having a "bad hair day" - went away, had a cup of coffee, worked it out with help from another forum! Forgot to multiply by 2 because they could have selected a female first. :p

  • All times are GMT -7. The time now is 08:21 AM.