e.

Cross multiply:

a.

The numerators must have the same units.

b.

The denominators must have the same units.

c.

Three of the four variables must be known.

(1)

In pharmacy, the EXPRESSION OF STRENGTH of the medication is

usually the first ratio of the proportion and this ratio is put in proportion to the amount of

medication to be made.

For example: If one aspirin tablet contains five grains of aspirin, then how

many grains would be required to make 40 tablets?

(2)

The EXPRESSION OF STRENGTH is "one tablet contains five grains

of aspirin" and should be written as the first ratio of the proportion:

IF 1 tablet =

THEN _____________

5 grains

(3)

Next, assign X its proper place in the second proportion. Because the

question asks, "How many grains?," the X is placed opposite the grains in the first

proportion.

IF 1 tablet

=

THEN _________

5 grains

X grains

(4)

In order for this to be a valid problem, the question has to tell how

many tablets for which we are calculating. The question asks to calculate the number of

grains in 40 tablets, therefore, the 40 tablets will be placed opposite the tablets in the

first ratio.

IF 1 tablet

=

THEN 40 tablets

5 grains

X grains

MD0802

1-36

Integrated Publishing, Inc. |