Section C - most examined topics

[Nancy]

Hi,

Section C is the least examined section. Therefore you need not spend too much time studying this section excepting chapter C2 - Statistics for business. You are likely to be asked the following questions on the topic

1. To calculate or identify from given options the correct values for 'a' , 'b' or Σx or Σy using the regression equation and

2. To identify what do the different variables in the regression equation signify

Apart from this you need to know what kind of relation does a given correlation coefficient 'r' signify between two variables - weak, strong or no correlation.

In Study guide C1 just remember the definition of expeted values and its business use. Study Guide C3 has been newly introduced and contains mainly the various uses of spreadsheets. You may give the least time allotment to this SG.

That is all for Section C and I hope some of you are reading and finding these posts useful. Best Luck!

[qitake]

Hello, I just joined.
thanks for the good tip,
I had a great difficulty to calculate r, i mean by math, i didnt get the same answer in first part. please help me to get it right. I know its basic math but- if you can please. thank you

[Sonal]

Hello, I just joined.
thanks for the good tip,
I had a great difficulty to calculate r, i mean by math, i didnt get the same answer in first part. please help me to get it right. I know its basic math but- if you can please. thank you

Do you mean to say that you are getting difficulty to calculate correlation r.
Steps to calculate r
1. present given X and Y values in tabular form
2. create new columns for XY(product of X and Y), X2(square of X) and Y2(square of Y) in the same table
3. find ∑ (total) for all columns
4. apply formula of correlation
Do remember that (∑X) 2 (square of ∑X) and ∑X2 (total of X square) both are different

[qitake]

Thank you Sonal,
I got stuck with question 11 @C part calculating b
b=11(13,467)-440x330 divided by
11(17,986)-(440)2
b=0,69171
I have tried but dont get the same answer, what is the order to calculate b?
please help

[Tammi]

Hi, qitake,

I have calculated it in the same order you have written there and the answer was :
b=0.69171

Here is the way I calculated it:

b=11(13,467)-440x330 divided by
11(17,986)-(440)2

b = (148,137 - 145,200) / (197,846 - 193,600)

b = 2,937 / 4,246

b = 0.6917098 (the same just not rounded)

[qitake]

Thank you Tammi
Have I missed something? as I got 440 x 440= 193600 not 193,600
where from this "," there?
that why i never get the right answer

[Tammi]

qitake, this "," is just for seperation to read it easily, not this one "."


and the answer in b is also with "." and not ","

So you haven't missed anything, you are calculating it correctly just don't mix "," and "."

[Sonal]

Thank you Sonal,
I got stuck with question 11 @C part calculating b
b=11(13,467)-440x330 divided by
11(17,986)-(440)2
b=0,69171
I have tried but dont get the same answer, what is the order to calculate b?
please help

Formula of regression:
b = (n∑XY - ∑X ∑Y)/n∑X2 - (∑X)2

That is
n sigma XY - sigma X sigma Y divided by n sigma X square – sigma X whole square

[Sonal]

Correlation and Regression are quite similar on the basis of calculations.

In regression also, you need to prepre table of X, Y, XY AND X2 (X square)

Calculate ∑ for all the columns, and then apply formula.

After calculating b, calculate a.

a can be calculate by following formula
∑Y/n - b(∑X/n)

Regression line: y = a + bx

[qitake]

Thank you everybody,
Ohh dear!
Tammi, Thanks for that point, i mean "," & "."
I read this number as thirteen comma four hundred sixty seven not as thirteen thousand four hundred sixty seven,,,,, Thats why I got wrong answer. Ehhee have to learn that it's just separator, (im not english).
thanks again