Reference no: EM132655156

A grad student has a culture of E. coli with a total volume of 700 mL, and OD reading at 550 nm of 1.35. He makes serial dilutions of the culture, starting with a transfer of 1 mL culture into 9 mL tryptone broth. Next, he transfers 0.1 mL of this dilution into 0.9 mL tryptone broth, and repeats this two more times to make a total of 4 serial dilutions. He then pipets 300 uL from the fourth dilution on an agar plate, spreads it over the surface, and puts the plate in an incubator to grow overnight. The next day, he counts 172 cfus (colony forming units) on the plate.

What is the dilution in the third tube? Answer using a proper format to express a dilution factor.

What is the dilution of cells spread onto the agar plate? Answer in decimal notation.