# Confusion over percentage volume

We've been told our lab report has to be written with "% v/v" instead of volume. I understand how to calculate it, however I'm unsure if I'm doing the right thing when it comes to using it later on. Example:

2ul 'W', 4ul 'X', 2.2ul 'Y', 1.8ul 'Z' is mixed in an eppendorf. It is incubated for 1 hour. After incubation, 0.95ml of 'B' is addded and then 150ul of the final mixture spread on plates.

I know the first bit would be: 20% v/v 'W', 40% v/v 'X', 22% v/v 'Y', 18% v/v 'Z' is mixed in an eppendorf.

But I dont know what to do when it comes to after the incubation?

I'm generally pretty good with this stuff but I've never had to think of it this way. Would, when 0.95ml is added, I do 0.95/0.95+2ul+4ul+2.2ul+1.8ul?

## 1 Answer

My assumptions:

1. 'ul' Refers to microlitres, be careful that the addition of B is in millilitres.
2. You are trying to calculate the % v/v that is being removed from the total solution at the end?

So before incubation the total volume is 2ul + 4ul + 2.2ul + 1.8 ul = 10ul (0.01ml) You are adding in 0.95ml, totalling 0.96ml. You are then taking 150ul (0.15ml) This equates to (0.15/0.96)*100 % = 15.6%