Linear regression

Willster1

I am really struggling with linear regression, every time i see that formula (Y = a + (bX)) i panic.

I don't understand this question on a mock exam at all, I got totally lost down a rabbit hole and just put random stuff in. The main part was the waste kg at the bottom, i tried to use the high low method to find the variable and fixed element- (23,650.00-23,256.25) / (q4-q1) but i have no idea now how they got £10,000 as the fixed element and 5.25 for the variable i'm just not getting it.

any help would be appreciated. attached question and my incorrect answers.

thanks

Pian32

So I'm reading through the whole question. First of all you want to have another look at the question:

What are the Quarterly forecasts for 20X4 in whole kgs?

You've used the correct method but the wrong x values remember X=0 is q1 of 20X0.

Following on from that the waste produced in q1 20X2

=2100+25x (x=9)

=2100 + 25 *9 = 2325 kg

and the waste produced in q4 of 20X2 (x=12) (There is a typoin the answer box it shouldn't say cost)

=2100+25* 12 = 2400 kg

What are the values of a and b in the cost equation?

Find b first:

b is the gradient of the line so you need to do (Change in Y)/(Change in x)

Change in Y = 23650-23256.25 = 393.75
Change in x = 2400-2325 = 75 (X in this question is number of kg of waste not the quarter number.)

b = 5.25

To find a use the q1 figures

23256.25 = a + 5.25*2325

a = 11050 (Are you sure they got 10,000?)

Check in q4

11050 + 5.25 * 2400 = 23650.



For linear regression take the following steps:

Identify what Y and X are. (Other letters could be used)
Find the change in Y and change in X
Use this to find b
Take b and put into equation for a value of x where you already know the y value.
Rearrange to find a
Check using the other set of x and y values.

Make sure you redefine y and x if the subject of the question changes (In this question x started as quarters but the later parts it was kg)