33% is the unknown concentration of the tube.
Explanation:
Concentration of stock of windex = 50%
concentration of bacteria = 500 microliter
nutrient broth = 1000 micro litre +500 microlitre of windex
concentration of bacteria is the volume of bacteria present in nutrient broth culture.
total volume in the tube is 1000
50% is the concentration of tube of bacteria and broth before adding windex.
After adding windex of 50 % concentration and the volume is 500 microliter which is only 250 microliter of windex rest is water.
33% is the concentration of the tube, which means it has 33% of bacteria in 1500 ml of solution.
