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

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

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

1-50

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