# microbiology question help watch

1. What volume of a 50 mg/ml stock solution of antibiotic would you need to also add to the dish if you wanted a final concentration of 25 µg/ml?

The dish is 31.86 cm cubed which I calculated previously. This question seems easy but I cant figure out how to do it?
2. ID use simple proportion
50mg - 1ml
50ug - x
No need for disk size

I may be wrong though
3. (Original post by Nottie)
ID use simple proportion
50mg - 1ml
50ug - x
No need for disk size

I may be wrong though
dont you need to take into account the volume of the antibiotic being added as that increases total volume and affects concentration.
4. (Original post by Year11guy)
dont you need to take into account the volume of the antibiotic being added as that increases total volume and affects concentration.
No. If you take some sea water into a glass the concentration of salt in the glass will be the same as in the sea
5. (Original post by Nottie)
No. If you take some sea water into a glass the concentration of salt in the glass will be the same as in the sea
but the glass is empty before putting the water in. Here the dish already has been filled and we will be adding more in increasing volume but you might be right.

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