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# help with this probability question would be much appreciated watch

1. 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
2. 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.
3. 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!?
4. thanks every1, makes sense now, was just a duh moment on my behalf.
cheers
xx
5. Oh man I am now a maths ninja.
6. when i get my next problem i'll be sure 2 ask u

thnx again x
7. 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.
8. 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
9. 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.)
10. thanks thats gr8

u guys r all so helpful

cheers
xx
11. (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
12. 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.
13. Goddamnit chewwy. The title of maths ninja now belongs to you.
14. (Original post by steve2005)
Probability of passing A and B=0.95
So Probability of passing A is greater than 0.9
15. (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.
16. ...darling.
It's going to take a lot more than a title to get into my pants, chewwy
17. (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!

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