_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.