[Tania Cossyleon]

The water at the beach on the lake front contains 9.6 parts per billion of Ecole. While swimming you swallow 1.0 liter of this water. How many grams of this bacteria did you swallow?
The only hint I have is that the density of the water is 1.053 g/cm^3:confused:

[ebaines]

As is often the case with this kind of problem, you need to be careful that the units you are using properly multiply out to get what you want. In this case you're trying to determine grams of Ecoli per liter of water. The only trick to this is knowing that there are 1000 cubic centimeters in a liter (stated another way: a cubic centimeter is the same as a milliliter). So one liter of water therefore weighs 1.053 g/cm^3 * 1000 cm^3/l = 1053 g/l. Assuming that the figure of 9.6 parts ecoli per billion is by weight, then for every billion grams of water there will be 9.6 grams of ecoli. You can now multiply as follows to get the units to work out:

1053 grams water/liter * 9.6 grams ecoli/10^9 grams water

which will give an answer in terms of grams of ecoli/liter of water.