14 Part 1: The World of Numbers
fish that are left, but before too long, you grasp subtraction: 8 – 4 = 4. Addition and subtraction
are just ideas of putting together and taking away that people developed to avoid having to keep
recounting.Addition
If addition is just a substitute for counting, why do you need it? The need is speed, especially
when the numbers get large. Counting 3 fish and 5 fish to find out you have 8 fish is fine, but
counting 3,000 fish and 5,000 fish would not be practical. When the addends, the numbers you’re
adding, get larger, you need a system to find the sum, or total, quickly. The place value system
allows you to add large numbers in a reasonable amount of time.DEFINITION
A sum is the result of addition. The numbers that are added are called addends.
In the equation 5 + 10 = 15, 5 and 10 are addends, and 15 is the sum.It’s important, of course, to learn basic addition facts, but the facts in the table and an
understanding of our place value system will get you through most addition problems.Basic Addition Facts
+ 12 34 5 6 7 8 9
1 2345678910
2 34567891011(^3456789101112)
(^45678910111213)
(^567891011121314)
6 789101112131415
(^78910111213141516)
8 91011121314151617
9 10 11 12 13 14 15 16 17 18
The left column and top row show the digits from 1 to 9. The box where a row and column meet
contains the sum of those digits.