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# Stats ques. watch

1. "I have a die with six faces numbered consecutively from 1 to 6. What is odd about it is that the probability of rolling the face with the number k is c*q^k, where c is a constant and q=0.96 What is the expected value of the roll of the dice"

I'm abit puzzled why I'm getting a wrong answer. The answer is 3.3811 according to mark scheme.
Don't you just integrate k*c*q^k between 1 to 6. As for c I got 0.191798..
2. (Original post by Mentally)
"I have a die with six faces numbered consecutively from 1 to 6. What is odd about it is that the probability of rolling the face with the number k is c*q^k, where c is a constant and q=0.96 What is the expected value of the roll of the dice"

I'm abit puzzled why I'm getting a wrong answer. The answer is 3.3811 according to mark scheme.
Don't you just integrate k*c*q^k between 1 to 6. As for c I got 0.191798..
Yikes.. integrating kcq^k wrt k sounds like a nasty business, how did you do it?
3. (Original post by Mentally)
"I have a die with six faces numbered consecutively from 1 to 6. What is odd about it is that the probability of rolling the face with the number k is c*q^k, where c is a constant and q=0.96 What is the expected value of the roll of the dice"

I'm abit puzzled why I'm getting a wrong answer. The answer is 3.3811 according to mark scheme.
Don't you just integrate k*c*q^k between 1 to 6. As for c I got 0.191798..
I've not completed this question myself, but the distribution is discrete, not continuous, so your integration should be a summation.

(Original post by SeanFM)
Yikes.. integrating kcq^k wrt k sounds like a nasty business, how did you do it?
For interest's sake, in this case you would write and proceed from there.
4. (Original post by joostan)
I've not completed this question myself, but the distribution is discrete, not continuous, so your integration should be a summation.

For interest's sake, in this case you would write and proceed from there.
Ah, I see. Not something you come across at A-level though I was thinking of using the definition of integration in the discrete case too, and it should get them the right answer. .
5. (Original post by SeanFM)
Yikes.. integrating kcq^k wrt k sounds like a nasty business, how did you do it?
I used Joostan method

(Original post by joostan)
I've not completed this question myself, but the distribution is discrete, not continuous, so your integration should be a summation.
*facepalm* ofcourse, I need to stop making these dumb mistakes lol

(Original post by SeanFM)
Ah, I see. Not something you come across at A-level though I was thinking of using the definition of integration in the discrete case too, and it should get them the right answer. .
Its my Uni-work, but it resembles some content that some able S2 students should be able to do so I posted anyway
Thanks so much for the help guys!

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