Answers: (1) 4 g
(2) 40,000 mg
(3) 3,470 ml
(4) 0.000142 g
(5) 0.25 g
(6) 3,000 ml
(7) 0.00145 kg
(8) 45,000,000 mg
(9) 250 mg
(10) 1 mg
1-38. GENERAL RULES
a. To add and subtract, all quantities must be expressed in the same units.
For example: Add 30 mg, 2.5 kg, and 7.0 g. Express the answer in grams.
30 mg
=
0.030 g
2.5kg
=
2500.000 g
7g
=
7.000 g
2507.03 g (Answer)
b. When dividing or multiplying, units should be changed if necessary, but,
general transfer and cancellation of units applies as in all mathematics.
For example: The strength of a drug is 5 mg per each milliliter of liquid. How
many milliliters must be administered to give the patient 0.05 g of the drug?
5 mg = 0.05 g
1 ml
X ml
NOTE:
Because corresponding units of each ratio of the proportion must be the
same, 0.05 g must be changed to milligrams.
The decimal must be moved three places to the right in changing from the
larger unit, the gram, to the smaller unit, the milligram. 0.05 g = 50 mg. Then:
5 mg =
50 mg
1 ml
X ml
5X
=
50 milliliters
X
=
10 milliliters
c.
Practical Exercises. Work the following problems:
(1)
Express the quantity 1.243 grams as:
(a) _____________mg
(b) _____________kg
(c) _____________mcg
MD0802
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