Unit Conversions: mass of uranium present in 1 mg of crust

[SCGirl]

Please help, I am getting really confused. Here is the question: It is estimated that uranium is relatively common in the earth's crust, occurring in amounts of 4 g/metric ton. A metric ton is 1000 kg. At this concentration, what mass of uranium is present in 1.0 mg of the earth's crust?

I tried this: 4g/1ton x 1ton/1000kg x 1kg/1000g x 0.001mg/g

Possible answers are: 4 nanograms, 4 micrograms, 4 milligrams, 4 x 10^-5 grams, or 4 centigrams.

I am not sure if I set up the problem right, because the way I did it the answer would be in terms of mg/g after everything is cancelled out. Please help and thanks in advance.

 

[wjm11]

It is estimated that uranium is relatively common in the earth's crust, occurring in amounts of 4 g/metric ton. A metric ton is 1000 kg. At this concentration, what mass of uranium is present in 1.0 mg of the earth's crust?

I tried this: 4g/1ton x 1ton/1000kg x 1kg/1000g x 0.001mg/g

Your last conversion factor (0.001mg/g) is wrong. It should be 1g/1000mg. The amount of U is:

1mg*(4g/1ton * 1ton/1000kg * 1kg/1000g * 1g/1000mg)
= 1mg*(4g/10^9mg)
= 4* 10^(-9) g
= 4 nanograms