Hi!

I know that might too easy for that group but, anyway I would like to ask:

I have a task: What is a volume of antibody you need to take, your ration should be 1/5000, 1/500, 1/250, my final volume is 12 ul.

My guess would be: examples: 1/5000=200 ul= (0,2*100)/12=160ul?

I have no idea whaty you are trying to say or what you are trying to ask. But certainly "200 ul" is NOT equal to "160 ul"!    You say the ratio is "1/5000", "1/500", "1/250" OF WHAT? Apparently you want the "volume of antibody" to be 1/5000 or SOMETHING but 1/5000 or WHAT?

 

My best guess at what you are trying to say:  1/5000  of something is 200 ul  so the "something" is 200(5000)= 1000000 ul or 1 l.  1/500 or that 0. ul or l.  1/250 of that is 4000 ul or 0.004 l.

(I assume your "ul" is a good replacemet for $\mu l$ or "microliters", one millionth of a liter.)