Turn on thread page Beta
    • Thread Starter
    Offline

    4
    ReputationRep:
    need help with all of this question...a worked solution would be really helpful


    7. A bag contains 4 red and 2 blue balls, all of the same size. A ball is selected at random and removed from the bag. This is repeated until a blue ball is pulled out of the bag.
    The random variable B is the number of balls that have been removed from the bag.
    (a) Show that P(B = 2) = 4/15 . (2 marks)
    (b) Find the probability distribution of B. (4 marks)
    (c) Find E(B). (3 marks)
    The bag and the same 6 balls are used in a game at a funfair. One ball is removed from the bag at a time and a contestant wins 50 pence if one of the first two balls picked out is blue.
    (d) What are the expected winnings from playing this game once? (4 marks)
    For £1, a contestant gets to play the game three times.
    (e) What is the expected profit or loss from the three games? (3 marks)


    I get you draw a tree diagram but how many trails? 2? I got part a) right but I don't know how ... can someone send me a worked solution please?
    • Thread Starter
    Offline

    4
    ReputationRep:
    trials**
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by N123456789)
    need help with all of this question...a worked solution would be really helpful


    7. A bag contains 4 red and 2 blue balls, all of the same size. A ball is selected at random and removed from the bag. This is repeated until a blue ball is pulled out of the bag.
    The random variable B is the number of balls that have been removed from the bag.
    (a) Show that P(B = 2) = 4/15 . (2 marks)
    (b) Find the probability distribution of B. (4 marks)
    (c) Find E(B). (3 marks)
    The bag and the same 6 balls are used in a game at a funfair. One ball is removed from the bag at a time and a contestant wins 50 pence if one of the first two balls picked out is blue.
    (d) What are the expected winnings from playing this game once? (4 marks)
    For £1, a contestant gets to play the game three times.
    (e) What is the expected profit or loss from the three games? (3 marks)


    I get you draw a tree diagram but how many trails? 2? I got part a) right but I don't know how ... can someone send me a worked solution please?
    What have you tried? You've got a right but you don't know how, I think you do know how but you've just got confused along the way. How did you calculate P(B=2)? For the probability distribution you could find all the values that B takes and their probabilities in a very similar fashion to P(B=2).
    • Thread Starter
    Offline

    4
    ReputationRep:
    for part a) I just multiplied along the branches of tree diagram and used trial and improvement to get the first answer now that I remember
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by N123456789)
    for part a) I just multiplied along the branches of tree diagram and used trial and improvement to get the first answer now that I remember
    Okay, trial and improvement got you there. So why was it 2/3 * 2/5? Can you interpret this result to understand how you would do it if you weren't given the answer, and so find the answers for the other values of B?

    (please quote me if you are replying so I can see that you have replied )
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by SeanFM)
    Okay, trial and improvement got you there. So why was it 2/3 * 2/5? Can you interpret this result to understand how you would do it if you weren't given the answer, and so find the answers for the other values of B?

    (please quote me if you are replying so I can see that you have replied )
    Spoiler:
    Show
    how did you get 2/3 and 2/5? on my tree diagram I got 2/6 x 4/5. I have no idea what I'm doing I would send an imagine of what ive done but it won't send
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by N123456789)
    Spoiler:
    Show
    how did you get 2/3 and 2/5? on my tree diagram I got 2/6 x 4/5. I have no idea what I'm doing I would send an imagine of what ive done but it won't send
    Why 2/6 and 4/5? What do those two things represent?
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by SeanFM)
    Why 2/6 and 4/5? What do those two things represent?
    the probability that a blue is chosen ?
    • Very Important Poster
    Offline

    21
    ReputationRep:
    Very Important Poster
    (Original post by N123456789)
    the probability that a blue is chosen ?
    So 2/6 is the probability of a blue being chosen in the first pick.. but that immediately rules out P(B=2) because the game is over as you have got a blue, hence B = ..
 
 
 

University open days

  1. University of Cambridge
    Christ's College Undergraduate
    Wed, 26 Sep '18
  2. Norwich University of the Arts
    Undergraduate Open Days Undergraduate
    Fri, 28 Sep '18
  3. Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 29 Sep '18
Poll
Which accompaniment is best?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.