How is 4.3 x 10^-3 the answer to this question?

A sample of air from a home is found to contain 6.2 ppm of carbon monoxide. This means that if the total pressure is 695 torr, then the partial pressure of CO is..................4.3 x 10^-3.

Just trying to learn the steps so that i can do this on my exam

Question

How is 4.3 x 10^-3 the answer to this question? 

A sample of air from a home is found to contain 6.2 ppm of carbon monoxide. This means that if the total pressure is 695 torr, then the partial pressure of CO is..................4.3 x 10^-3. 

Just trying to learn the steps so that i can do this on my exam

aaronq · Answer

6.2 ppm (parts per million) means that in 1 million parts 6.2 of those are CO.

This calculation is just a proportionality, for example if i said i had 10 oranges and 20% are rotten, then 10 oranges *0.2 = 2 oranges are rotten.

For this it's:  $\sf 695~torr*\dfrac{6.2}{1000,000}=4.3 x 10^{-3}$