Prior to cross multiplying, make sure that corresponding units in each
ratio are the same. Then, use the following steps
(a) Set up the proportion:
IF 1 tablet =
THEN 40 tablets
(b) Cross multiply:
1 (X) = 5
(c) Solve for X: X = 200
(d) Refer back to step 1 to find the units of X. The units for X are
grains. Therefore, the answer is 200 grains.
The most common mistake people make is failing to label units.
Labeling units will assure that corresponding units of the proportion are the same.
Solve this problem:
How many milliliters of tetracycline suspension, which contains 250 mg of
tetracycline in each five milliliters, must be administered to give a patient 150 mg?
(b) Assign the X value to its proper place in the second proportion:
(c) Find the third known value: