Combinations of Random Variables Awkward Variance Questions

But in edexcel EX4a they do a similar thing but don't include the coefficient being squared in the variance

Thoughts?

1. Which module?

2. Show us. Why do you think they haven't included the coefficient being squared?

3. It's probably because you have to add the variances up, so: 225 + 225 + 225 + 225, and then divided that by 16. Which is $\frac{4 \times 225}{16} = \frac{225}{4}$. But I can't say that for sure because you haven't shown anything.

In the future, please try to provide some sort of link or picture or anything instead of just paraphrasing.

S3.

imgur is playing up it corresponds to the bottom of the page 3 s3 guide - assuming you possess it.

It is the part where you deduce whether the operation is Var(12X) ir 12^2(Var X)

You've given me two different questions now. Which is it? The weight of men or bottles?

I Get How The Operation Works With The Men

Although I Am Unsure Of The Operation On The Bottles. Could You Please Tell Me That When:

I Have 12 Bottles, How do you distinguish between doing 12Var(X) and Var(12X) you explained the men question, thanks.

You could have said that instead of just ignoring my post.



It's 12 bottles, so $B_1 + B_2 + \cdots + B_{12}$ Hence you would do:

Lastly do you know of any learning material on this topic. There is a plethora of questions availiable, however scarce learning material I would say.

I thought the textbook was more than enough. I don't know of anything else.

Okay thanks for your help. It will have to do.

No worries.

I really see what you have done, you modelled it as the variable being multiplied as in 12*(all the bottles) where I was doing bottle1+bottle2+...+bottle12.

No, I'm adding as well. It's just that when you add two random variables, you add their variances. But instead of me adding all 12 variances, I just multiplied by 12 instead.

Thanks.

You could have said that instead of just ignoring my post.



It's 12 bottles, so $B_1 + B_2 + \cdots + B_{[b]12[/b]}$ Hence you would do:

How did you know to divide by 12 here?

What's the mean? "sum all the terms and divide by the number of terms".

The worked solution on page 4 of the edexcel book says to do 12Var(X) are they wrong?

How did you know to divide by 12 here?

I see what you are saying here.

If you are given two distributions for men and women, eg M~N(a,b) and W~N(c,d) and you are asked to find the probability of the men's weight being greather than 1.5 times the woman's weight, then we can call that a new distribution (say U), and M-1.5W = U ~ N (a - 1.5c, b + 1.5^2d) (and we are looking for P(U>0) but that is not the point I am trying to illustrate )

When you're just adding people's weights up rather than multiplying the distribution by a number, you don't need to use Var(ax) = a^2Var(x).