A set of y-values is transformed (in order to yield a better linear fit) by taking the natural logarithm of each value. The regression of ln y on x is then computed as ln y=-3.1+2.5x. What is the predicted value of y when x=3?

Question

loser66 · Answer

just replace x =3 in ln y = ....
then take e both sides to get y

hockeychick23 · Answer

@iGreen i got 4.4 could you check my answer please?

hockeychick23 · Answer

@rational can you help me with this please?

rational · Answer

$$\ln y = 4.4$$
$$y=?$$

hockeychick23 · Answer

i looked up how to do it and by the steps this is what i got: y=e^2.5x-3.1= (e^2.5)^xe^-3.1= EXP(2.5)^xEXP(-3.1) i just don't know what to do next

hockeychick23 · Answer

and I'm not sure if 4.4 is right that was the solution that i thought might be right

rational · Answer

$$\ln y =4.4  $$
is same as
$$y=e^{4.4}$$

rational · Answer

plug that into calculator

rational · Answer

http://www.wolframalpha.com/input/?i=e%5E4.4

hockeychick23 · Answer

oh so its 81.45? I'm not sure if the 4.4 i got was right to start though

rational · Answer

Correct.
lny = 4.4 is also correct

hockeychick23 · Answer

oh so the answer is 81.45, thanks! (sorry I'm sorta bad with this)

rational · Answer

remember :
$$\ln y = a$$
is same as
$$y=e^a$$

where $e$ is an irrational number : $2.718\ldots$

hockeychick23 · Answer

oh ok does that mean I'm wrong?

rational · Answer

you're right, 
why do u think you're wrong

hockeychick23 · Answer

i thought i had to do something with the 2.718 sorry

rational · Answer

wolfram did that for you

rational · Answer

wolfram knows that e = 2.718...

hockeychick23 · Answer

ok awesome thanks!