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hockeychick23
 one year ago
Find the expected value of the number of questions you'd get right by guessing. What are the variance and standard deviation?
hockeychick23
 one year ago
Find the expected value of the number of questions you'd get right by guessing. What are the variance and standard deviation?

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hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1@jim_thompson5910 can you help me please?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2X = number of correct questions dw:1433396801483:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2multiply X and P(X) to form the X*P(X) column of values

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2now add up the values in the X*P(X) column and you will get the expected value

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2so the expected value is 0.5 which means, you expect (on average) to get 0.5 questions right if you randomly guessed

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2now onto the second part "What are the variance and standard deviation? "

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2you're going to have 2 additional columns. I'm going to erase the X*P(X) column to make room

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2instead I'm going to have X  mu and (X  mu)^2 dw:1433397803766:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2mu = expected value = 0.5

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2oh wait, there's one more column needed the P(X)*(Xmu)^2 column dw:1433397806736:dw

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1oh ok, so do i find the mean of p(x)?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2you're asking about the value of mu? mu = 0.5 and it was found when you computed the expected value

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1oh ok sorry it took me a while to calculate the numbers

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2this is what I'm getting

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I see the typo you made. Look at the bottom row, last column

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2you should have (20.5) and not (10.5)

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1sorry i pasted the wrong table this is what i got

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2btw if you have excel or open office (it should work in there too), you can type in formulas like you see attached

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2that way you can automate things a bit

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2now add up everything in the P(X)*(Xmu)^2 column, you should get 0.375

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.20.375 is the variance take the square root of the variance to get the standard deviation

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1standard deviation= .61237243569 variance= 0.375

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1ok thanks so much! i have a question pertaining to the same data that i need help with if you can help me with it: Let's say that for one of the two questions you can narrow the answer choices down to three. Now your chance of getting that question right by guessing is about .33. What is the new expected value for the number of questions you'd get right by guessing? What are the new variance and standard deviation of this random variable? Drawing another tree diagram and making another probability distribution table may help you answer this question. I'll give you another medal

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2were you able to get started on this one? or no?

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1sort of but I'm not sure if i did it right, i did

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I made question 1 have P(correct) = 0.33 and question 2 has P(correct) = 0.25 dw:1433401116557:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2are you seeing how I'm getting these values?

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1ohhh yes thanks!

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2so here is getting 0 questions correct dw:1433401932751:dw ie getting both wrong

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.20.0825 is cut off, but that's getting both correct dw:1433401967587:dw

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1Ok so 0.5025 is the probability of getting 0 correct and 0.0825 is getting both correct.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2and the other values are added to get the probability of getting exactly 1 correct so that gives us this new table dw:1433402014075:dw

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1Ok so would i need to find the expected value again?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2this is what I get

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2You have 0.825 instead of 0.0825

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2So I'm getting an expected value of 0.58 and a variance of 0.4086 standard deviation = sqrt(variance) = sqrt(0.4086) = 0.63921827 (approximate)

hockeychick23
 one year ago
Best ResponseYou've already chosen the best response.1ok now I'm getting that too, thanks! (I'm going to post something and tag you in it to give you another medal)

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2that's fine, it doesn't matter about the medal thing lol

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I'm glad it's making sense now
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