Help with regression lines

- brandonw998

Help with regression lines

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- brandonw998

##### 1 Attachment

- brandonw998

I can't figure out how to get the Predicted cost part

- jim_thompson5910

how did you find 0.08 in that last box?

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- brandonw998

I have done the question like 6 times and it's always 0.08

- jim_thompson5910

what kind of calculator do you have?

- brandonw998

TI-84 Plus CE

- brandonw998

I enter in the data in L1 and L2 but can never get the answer they get

- jim_thompson5910

idk what the CE means, but I have a TI84 plus, so I guess that works

- jim_thompson5910

so you have your data into L1 and L2
did you do a LinReg ?

- brandonw998

Yes

- jim_thompson5910

ok it should say something like ax+b or a+bx
and then spit out what a and b are

- brandonw998

b=-467.213 but the answer is always between like 164 to 166

- jim_thompson5910

hmm let me try, one sec

- brandonw998

I guess what's the predicted cost when the miles is at 0.08?

- jim_thompson5910

ok I'm getting 0.08 now

- jim_thompson5910

and I'm not getting a number between 164 and 167
but I'm getting pretty close to it

- brandonw998

How did you get 0.08?

- jim_thompson5910

well I got 0.07877 approx which rounds to 0.08

- brandonw998

How?

- brandonw998

In LinReg?

- jim_thompson5910

yeah using that function

- brandonw998

I don't see it in mine :(

- jim_thompson5910

it's in the calc menu after you hit the stat key

- brandonw998

Calc 4?

- jim_thompson5910

yeah

- jim_thompson5910

btw make sure your "miles" is in the L1 column

- jim_thompson5910

if you put "miles" in the L2 column, you'll have to type in `LinReg(ax+b) L2,L1`

- brandonw998

Ohh really? I've been putting it in L2 that must be the problem

- brandonw998

Why must the miles go first?

- brandonw998

Now I got it a=0.07877

- brandonw998

and b is 162.95

- jim_thompson5910

because the equation is
cost = ____ + ____ * (miles)
miles is the input

- brandonw998

Oh I see so I was doing it backwards

- jim_thompson5910

well they put the columns in the wrong order (probably to throw you off)

- brandonw998

So Predicted cost should be 162.96?

- brandonw998

162.95

- brandonw998

I actually have to do this problem again since I already restarted it

- jim_thompson5910

no that value goes in the missing box

- brandonw998

Oh right

- brandonw998

Thanks man! I guess I was getting it wrong because I was entering in L1 and L2 backwards. I have been so confused for over an hour. Thank you!

- jim_thompson5910

yeah I made the same mistake but swapping the columns or entering `LinReg(ax+b) L2,L1` addresses the issue

- brandonw998

Oh okay

- brandonw998

Thank you :D

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