Bacterial Genetics

[Maxtor]

Can anybody solve this problem?

I have no idea how to approach this one.

 

Numbers of bacterial in a suspension are usually so large that single colonies would be impossible to observe without suitable dilution. The usual dilutions are 100-fold, in which 0.1 ml of the suspension is mixed with 9.9 ml of dilution buffer; or 10-fold, in which 0.1 ml of suspension is mixed with 0.9 ml of suspension buffer. Usually serial dilutions are necessary, in which the suspension is diluted once into dilution buffer, the resulting suspension mixed

thoroughly and diluted a second time, the resulting suspension mixed thoroughly and diluted a third time, and so forth. The serial dilution factors multiply, so, for example, two 100-fold and two 10 fold dilutions yield an overall dilution factor of 100 x 100 x 10 x 10 = 1 million.

A suspension of bacteria contains 5 x 107 (ie, 50 million bacterial) per ml. You need to order 10 ml pipettes at $100 each, 1 ml pipettes at $10 each and 0.1 ml pipettes at $1 each from the storeroom. No pipette can be reused. What is the cheapest combination to measure out a sample of about 500 bacteria?