When converting from one system to another, you  must know the relationship or approximate equivalency between the measurements of each system.  This relationship is outlined in the Drug Dosage Lab document on page 10.  YOU MUST KNOW THESE CONVERSIONS. 

To work a problem: 

1. set up a ratio with the left hand side being the known conversion equivalency
2. put labels on right hand side to match labels on left hand side
3. add in the numbers from the problem into the appropriate location in the equation based on the labels
4. cross multiply top on left to bottom on right and bottom on left to top on right
5. solve for x
   

Example problem #1:  Convert 3 gr to mg.

The known relationship between grains and milligrams is that 1 gr = 60 mg.  Set up a ratio with the known conversion information as the left hand side of the ratio and put labels in on right hand side of ratio to match labels on left. 

   1 gr    =    ___ gr
   60 mg            mg


Now, look back at your problem and see if you have numbers to "plug in" on the top or the bottom of the right side of the ratio.  Put the number in the appropriate location and add in an "X" into the vacant spot.  In this example, you have 3 gr; therefore, that will go in the top of the ratio and X goes into the bottom.

     1 gr    =     3 gr
    60 mg         X mg

Cross multiply top side on left with bottom side on right and bottom side on left with top side on right.  Drop the labels at this point.

       1 X = 180

Look back to your ratio and see what label you had with X and that is the label with the answer.  X = 180 mg.  You have determined that 3 grains is equivalent to 180 mg.


Example problem #2:  186 pounds =  _______ kg


     1 kg   =   X kg
     2.2 lb      186 lb

         2X = 186

         2x   =    186
          2            2

          X   =    84.55 lb

Final answer would be 85 lb because of PCC calculation rules that state for weights 100 pounds or more, the final answer should be to the nearest whole number.