The lethal dose of potassium cyanide taken orally is 1.34 mg per kilogram of body weight. How much of the lethal dose of potassium cyanide would a 175 lb person have to take?
1 kilogram (kg) is equal to 2.205 pounds (lb).
To find the kg of the person, you take their weight in lb's and divide it by the amount that's equal to 1 of the unit that you want.
As you can see, the units of the lb neatly cancel, leaving you with just the kg.
Now that you have the kg of the person, all you have to do is multiply it by the lethal dose of 1.34mg/kg.
Again, you can see how the units of kg are nicely cancelled.