Ratio represents a quantitative relationship between two quantities.
Ratio and
proportion
Ratio
represents a quantitative relationship between two quantities. It can be
expressed as a fraction (e.g., ½, ¼, and so on) or as a ratio (e.g., 1:2, 1:4,
and so on).
A
proportion represents the equality of two ratios. Thus,
1/2=2/4
The
equality of two ratios can be checked by cross multiplying the numerator of the
first with the denominator of the second. For example,
1/2
= 2/4 but 1/2 ≠ 2/6
because
1× 4 = 2 × 2 but 1× 6 ≠ 2 × 2
Proportions
are commonly utilized to find an unknown quantity or variable when three other
related quantities or variables are known. For example,
If
x/4 = 2/9 , then x = (2 × 4)/9 = 8/9
In
these calculations, caution must be exercised to ensure that the numera-tors
and denominators have the same units on both sides of the proportion. For
example, if the pharmacist wishes to substitute 100-mg strength tablets with
200-mg strength tablets for a patient who was prescribed four tablets of 100-mg
strength, then the number of tablets of 200-mg strength can be calculated as:
A
good practice in carrying out these calculations is to always label the units
in the proportions.
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