Quantcast

A community for students. Sign up today!

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

sleung

  • 10 months ago

A student who is taking a 30 question multiple choice test knows 24 of the answers. If the student doesn't know the answer, he chooses uniformly from 1 of 5 choices. Given that he gets a randomly chosen question right, what is the probability he guessed on the question?

  • This Question is Open
  1. elvisg1993
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    30!/(24!) * 1/5

  2. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    How'd you get that elvis?

  3. dumbcow
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    conditional probability \[P(A | B) = \frac{P(A and B)}{P(B)}\] probability he guesses and gets it right = 1/5 probability the question is right = (24+6/5)/30

  4. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    My exam says that the answer is 1/21. How do u get that?

  5. dumbcow
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    oh sorry my P(AB) is wrong, it should be 1.2/30 \[\frac{\frac{1.2}{30}}{\frac{25.2}{30}} = \frac{1.2}{25.2} = \frac{1}{21}\]

  6. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Thanks a lot.

  7. dumbcow
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    yw

  8. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    How'd you get 1.2 and 25.2? Still not quite clear on that.

  9. dumbcow
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    1.2 is the avg number of questions guessed correctly ---> 6*(1/5) 25.2 is avg total num of correct questions ---> 24 + 6/5

  10. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Thanks so much

  11. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    For 0<x<y<z<1, the joint density of (X,Y,Z) is given by f(x,y,z)=48xyz. Find P(Y>1/2). I got .78, but my exam says it's .84.

  12. dumbcow
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[48 \int\limits_.5^1 \int\limits_y^1 \int\limits_0^y (xyz) dx dz dy\] \[= 48 \int\limits_.5^1 \int\limits_y^1 \frac{y^3 z}{2} dz dy\] \[= 48 \int\limits_.5^1 (\frac{y^3}{4} - \frac{y^5}{4}) dy\] \[= 12(\frac{y^4}{4} - \frac{y^6}{6}) |_.5^1\] \[= 1 - \frac{10}{64} = \frac{27}{32}\] = 0.84375

  13. dumbcow
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    how did you go from pre-calc probability to multi-variable calculus?? lol

  14. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Haha, don't know - guess i should've asked that in the calc section. I was asked to find a probability though.

  15. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Insurance losses L in a given year have a lognormal distribution with L=e^X, where X is a normal random variable with mean 3.9 and standard deviation 0.8. If a $100 deductible and a $50 benefit are imposed, what is the probability the insurance company will pay the benefit limit given that a loss exceeds the deductible?

  16. sleung
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    A fair 6-sided die is rolled 1,000 times. Using a normal approximation with a continuity correction, what is the probability the number of 3's rolled is greater than 150 and less than 180? I'm supposed to get .78, but instead I'm getting .81.

  17. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Ask a Question
Find more explanations on OpenStudy

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.