# find the Variance

• March 10th 2011, 01:55 AM
ZOOZ
find the Variance
is known that the Tomato crop (in ton) in some farm are Sampled for 10 years.
the Standard deviation of the crop was 2 ton.
the Income (Y) from the Tomato Depends on the crop (X)
according to following connection Y=3X-2. the Variance Income from the Tomato in this Sampled is ?

if i know that the Standard deviation is 2 so i just need to do 2^2 to get the Variance yes?

and 1 more Question: the Value of Pearson product-moment correlation coefficient between the crop and the Income is?
how i can solve it?

thanks.
• March 10th 2011, 03:39 AM
mr fantastic
Quote:

Originally Posted by ZOOZ
is known that the Tomato crop (in ton) in some farm are Sampled for 10 years.
the Standard deviation of the crop was 2 ton.
the Income (Y) from the Tomato Depends on the crop (X)
according to following connection Y=3X-2. the Variance Income from the Tomato in this Sampled is ?

if i know that the Standard deviation is 2 so i just need to do 2^2 to get the Variance yes?

and 1 more Question: the Value of Pearson product-moment correlation coefficient between the crop and the Income is?
how i can solve it?

thanks.

The formula for Var(aX + b) should be given in your textbook or class notes. Have you looked for it? (You will also find it using Google).

The procedure for calculating the Pearson product-moment correlation coefficient should also be given in your class notes or textbook (or found using Google). Where are you stuck?
• March 10th 2011, 11:50 AM
ZOOZ
well
i am not study this in class yet, this why i asked it here.

tell me if i correct if i will say that the Variance will be 4 because the Standard deviation of the crop was 2 ton, so i only need to do 2^2=4 yes?

and for Pearson product-moment correlation question can you give me any direction?

thank you.
• March 10th 2011, 01:56 PM
mr fantastic
Quote:

Originally Posted by ZOOZ
i am not study this in class yet, this why i asked it here.

tell me if i correct if i will say that the Variance will be 4 because the Standard deviation of the crop was 2 ton, so i only need to do 2^2=4 yes?

and for Pearson product-moment correlation question can you give me any direction?

thank you.

Perhpas it would be best to wait until you have started your studies in this class. That way, your teacher can give you the instruction you need to understand how to answer questions like these.
• March 11th 2011, 01:27 AM
ZOOZ
:) ok maybe you are right
still thank you.
• March 11th 2011, 01:56 AM
ZOOZ
well i still want to try one more try:
if is known that the Standard deviation of the crop(X) was 2 ton so the Variance of it will be 4 so if i use Y=3X-2 and put there those numbers:
Y=3*4-2=10 so the Variance Income from the Tomato in this Sampled will be 10 ?

thanks.
• March 11th 2011, 02:21 AM
Unknown008
No, it's a little more complicated than that.

If you have

Y = aX + b

where a and b are constants;

Var(Y) = Var(aX + b)

Var(Y) = Var(aX) + Var(b)

Var(b) is zero because the variance of a constant is zero, right?

So, Var(Y) = Var(aX)

Here is something to be careful, Var(aX) = $a^2Var(X)$

So,

$Var(Y) = a^2Var(X)$
• March 11th 2011, 02:26 AM
ZOOZ
OK so if i use this:var(aX+b)=a^2var(X)
i get 9*4=36 and this is the answer ?
"ar(b) is zero because the variance of a constant is zero, right" that was helping.

thanks.
• March 11th 2011, 02:38 AM
Unknown008
Yes, that is the variance of Y.
• March 11th 2011, 04:56 AM
ZOOZ
GREAT.

thank you very much.
• March 20th 2011, 02:07 AM
ZOOZ
hi.
according to the same information that i gave in this question i can say that the Pearson correlation coefficient will be 1
because we have Absolute linear relationship.

i almost sure is 1 but about the reason i not sure 100%.

thanks.