Simple denominate numbers.—When we speak of measures, whether they are of money, extension, time, or weight, we use terms like 5 dollars, 4 yards, 3 hours, or 10 pounds to express the quantity we are talking about.
Sometimes we use two or more terms or names to express the measure, as 3 hours, 15 minutes, 10 seconds; 4 gallons, 3 quarts, 1 pint. These are compound denominate numbers.
The chief differences between compound numbers and simple numbers is, that with the exceptions of United States money, and the metric system of weights and measures, the denominations of compound numbers do not increase or decrease by the scale of ten.
Reduction.—Reduction of Compound Numbers is the process of changing them from one denomination to another without altering their value.
Reduction Descending is changing the denomination of a number to another that is lower, as: 2 hours = 120 minutes; 2 feet = 24 inches.
Reduction Ascending is changing the denomination of a number to another that is higher, as: 120 minutes = 2 hours; 24 inches = 2 feet.
Rules for Addition of Denominate Numbers
First.—Write the names of the different units to be used in addition, placing them in a horizontal row, the largest to the left.
Next.—Write the numbers of each unit to be added, below the names of the units, each in its proper place.
Then.—Add and place each sum below the column added.