DIMENSIONAL ANALYSIS METHOD
Dimensional analysis is a systematic method of problem solving that avoids the use of formulas. It is much easier to learn one method that works for all problem solving, than to try to figure out which formula you need to use, and which numbers go where. It requires a working knowledge of conversion factors and equivalencies. Equivalents are factors that are equal to each other. For example: [3ft =1 yard] is an equivalent or has the same value. Flipping the equation [1 yard=3ft] does not change its value. The same is true with [36 inches=1 yard] and [1 yard=36 inches]. Conversion Factors are equivalents that are necessary for moving between the different systems of measurement [apothecary, metric, and household].
1. Carefully read the problem. Determine the GIVEN QUANTITY (which is given to you in the problem).
2. Determine what unit the WANTED
QUANTITY (answer) is supposed to be in (ml or mg or minutes, etc.)
3. Determine what CONVERSION
FACTORS you will need to use. Some
may be given to you in the problem (like how many mg/ml) while others we expect you to
know (like how many cc in a teaspoon).
4. SET UP:
Dimensional Analysis problems are set up like fractions, with a numerator (top
number/s) and a denominator (bottom number/s). You need to set up the problem so that the
unwanted units are canceled out. If you are
given mg on top, and you really want the answer in ml, you would set up the problem using
a ml to mg conversion (given in the problem) and place mg on the bottom, so the mg cancel
out. [I know this really doesn’t make
since but hang in there, it gets easier as you work the problems].
5. Cross out the units that cancel out,
leaving nothing but the wanted quantity.
6. Do the basic math. Solve the problem by using basic math (no algebra
needed). Multiply the numbers across. Divide the top number by the bottom number. You now have the correct answer!
A client is admitted to the hospital. The doctor orders Ceclor 500mg. The medication bottle states that there are 400 mg of Ceclor in 5 ml of fluid. You will need to calculate the number of ml you will give the patient.
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