Uses Of Subtraction
The most familiar meaning for subtraction is called "take away." To find the answer if you take 5 eggs from a dozen, you subtract: 12 - 5 = 7.
Subtraction is also used to compare two numbers. When one wants to know how much colder -7.3° is than 13.8°, one computes the difference -7.3 - 13.8 to get -21.1°.
A third use of subtraction is to figure out a missing addend. If one has a certain sum of money, say $45.20 and wants to buy an article costing $85.50, subtraction is used to compute that needed amount: 85.50 - 45.20.
J. Paul Moulton