probability distribution
Message posted by Cathie (via 161.184.204.204) on November 11, 2001 at 1:11 PM (ET)

I am on my 3rd unit in stats math Probability Distribution and my assignment is asking an assortment of questions, I'm assuming preparing me for my mid term, however, i am so lost in this it isn't even funny. the question is: Out of a random sample of 33 students of which 10 are in their 30's, 15 in their 40's, 5 in their 50's and 3 in their 60's.Let x be the age.
A) probability the student is in their 30's..my answer is simply 10/33..is it correct?
B)probability student is 50 or 60..my answer is 8/33.
C)expected value of x...this I'm not sure on at all
thank you for your time!!

READERS RESPOND:
(In chronological order. Most recent at the bottom.)

Re: probability distribution
Message posted by Tomi (via 154.32.143.194) on November 11, 2001 at 8:04 PM (ET)

For the expected value, you use E(X) = sum (P(X_i)*X_i)

Assume that the mid-range value of "people in their 30's" is 35 etc.

Expected value = 35*(10/33) + 45*(15/33) + 55*(5/33) + 65*(3/33) = 350/33 + 675/33 + 275/33 + 195/33 = 1495/33 = 45.303 = 45 years (nearest year).

15 in their 40's, 5 in their 50's and 3 in their 60's.Let x be the age.
A) probability the student is in their 30's..my answer is simply 10/33..is it correct?
B)probability student is 50 or 60..my answer is 8/33.
C)expected value of x...this I'm not sure on at all
thank you for your time!!