RATIO AND PROPORTION
INTRODUCTION
"Ratio and proportion" is discussed early In the course because most
of the problems dealing with pharmaceutical calculations can be restated
or can be broken down to a simple ratio and proportion problem. The principles
discussed in this section will be of great value in solving most problems.
DEFINITIONS
a. Ratio: A ratio is the relationship of two quantities. A ratio may
be expressed as a ratio (1:8, 1:200, etc.) or as a fraction (1/8, 1/200,
etc.).
b. Proportion: A proportion is the equality of two ratios.
EX: 1/2 = 3/6
c. A check as to the equality of two ratios can be made by cross multiplying.
Multiply the numerator of the first ratio times the denominator of the
second ratio. Then, multiply the denominator of the first ratio times the
numerator of the second ratio. If the ratios are equal, the results of
the cross multiplication will be the same.
EX: 1/2 X 3/6 => 3 x 2 =1 x 6
6 = 6
d. The products of the cross multiplication are always equal in a proportion;
if one factor of either ratio is unknown, it may be solved for by
substituting X for the unknown factor in the proportion.
CONDITIONS WHICH MUST BE MET
a. The numerators must have the same units.
b. The denominators must have the same units.
-
Three of the four variables must be known.
Home