Concentration of a gas?

Question

If I drop an eyedropper drop of ordinary unleaded petrol into a container of exactly 1 litre, once it evaporates, what will the concentration of petrol vapour be, measured in PPM.

Answer 1

First try to measure the volume of 100 eyedropper drops, to figure out the volume of one eyedropper drop. Afterwards this problem can be solved easily.