In the Reaction CO+2H²-->CH³OH, 1.27 g of CH³OH are made in the lab. The Percent yield of this reaction is___.

Would the answer be 42?

Pick a number, any number. You need to know how much CO OR H2 you started with. As it stands, the answer is indefinite.

so... it dosent matter what number i answer with?

If the question is as you posted it, no, I don't think any answer will do.
Technically,
%yield=(1.27/theoretical yield)x100 = ??

Since you don't have a number to put into the equation for theoretical yield, I would answer "indeterminate" or "depends upon theoretical yield".

ooooh, i Get it! sounds simple.. Thanks!!

You're welcome! I'm glad I could help clarify it for you. It's important to remember that calculating the percent yield requires knowing the theoretical yield, which is the maximum amount of product that could be obtained based on the stoichiometry of the reaction. Without that information, it's not possible to determine the percent yield accurately. Feel free to ask if you have any more questions!