Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    i've got a problem with this maths question involving probabilities. i've never studied decision maths above gcse, so having a little difficulty.
    thanks in advance for any help.

    explain fully why there must be a mistake with the following statement:

    the probability that an ambulance service will receive more than 10 calls on a certain day is 0.53 and the probability that it will receive more than 12 calls is 0.60.

    ??? lol, any help would really be appreciated.
    thanks
    Offline

    7
    ReputationRep:
    Probability that it recieves more than 10 calls = probability that it receives 11 or 12 calls + probability that it receives more than 12 calls.

    0.53 = probability that it receives 11 or 12 calls + 0.60
    probability that it receives 11 or 12 calls = -0.07
    But probabilities cannot be less than 0.
    Offline

    15
    ReputationRep:
    p(more than 12 calls) + p(12 calls) + p(11 calls) = p(more than 10 calls)
    p(12 or 11 calls) = 0.53-0.6 = -0.07. how can you have a negative probability!?
    • Thread Starter
    Offline

    0
    ReputationRep:
    thanks every1, makes sense now, was just a duh moment on my behalf.
    cheers
    xx
    Offline

    7
    ReputationRep:
    Oh man I am now a maths ninja.
    • Thread Starter
    Offline

    0
    ReputationRep:
    when i get my next problem i'll be sure 2 ask u

    thnx again x
    Offline

    7
    ReputationRep:
    You can just post it up on the board, and I will be sure to get there first. That is the beauty of being a maths ninja.
    • Thread Starter
    Offline

    0
    ReputationRep:
    perfect coz im confused by the next question... you may have realised im not 2 gr8 at this ... me feel stupid... but its better 2 ask and learn than not 2 ask at all.. so...

    explain why its wrong, as before:

    the prob. that a student will pass exam A is 0.90 and the prob. he will pass exams A and B is 0.95

    ???

    something 2 do with the prob. of passing both should be less than the prob. of passing just one of the exams...?
    not sure

    help maths ninja lol
    Offline

    15
    ReputationRep:
    i'm a maths... um... solja.

    p(AnB) = p(A) * p(B|A)

    so p(B|A) = 0.95/0.9 > 1. you can't have probabilities greater than 1...

    (p(B|A) means the probability of B occuring, given A has occured.)
    • Thread Starter
    Offline

    0
    ReputationRep:
    thanks thats gr8

    u guys r all so helpful

    cheers
    xx
    Offline

    14
    ReputationRep:
    (Original post by loumatti)
    perfect coz im confused by the next question... you may have realised im not 2 gr8 at this ... me feel stupid... but its better 2 ask and learn than not 2 ask at all.. so...

    explain why its wrong, as before:

    the prob. that a student will pass exam A is 0.90 and the prob. he will pass exams A and B is 0.95

    ???

    something 2 do with the prob. of passing both should be less than the prob. of passing just one of the exams...?
    not sure

    help maths ninja lol
    Probability of passing A and B=0.95
    So Probability of passing A is greater than 0.9
    Offline

    7
    ReputationRep:
    Try drawing a venn diagram. You will get an area of 0.95 being part of an area of 0.90, when clearly part of an area cannot be greater than the whole area itself.
    Offline

    7
    ReputationRep:
    Goddamnit chewwy. The title of maths ninja now belongs to you.
    Offline

    15
    ReputationRep:
    (Original post by steve2005)
    Probability of passing A and B=0.95
    So Probability of passing A is greater than 0.9
    with all due respect... your answers in this thread have been ****.
    Offline

    15
    ReputationRep:
    (Original post by Speleo)
    Goddamnit chewwy. The title of maths ninja now belongs to you.
    don't worry, i'm happy to continue being a maths solja. you may remain a maths ninja, darling.
    Offline

    7
    ReputationRep:
    ...darling.
    It's going to take a lot more than a title to get into my pants, chewwy :p:
    Offline

    16
    ReputationRep:
    (Original post by Speleo)
    Try drawing a venn diagram. You will get an area of 0.95 being part of an area of 0.90, when clearly part of an area cannot be greater than the whole area itself.
    exactly...

    Venn Diagrams all the way!
 
 
 
Poll
Black Friday: Yay or Nay?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Equations

Best calculators for A level Maths

Tips on which model to get

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

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.