20 Part 1: The World of Numbers
CHECK POINT
Use compatible numbers to help you complete each addition problem.- 18 + 32 + 97
- 91 + 74 + 139
- 158 + 482 + 327 + 53
9. 71,864 + 34,745 + 9,326
10. 9,865 + 7,671 + 8,328 + 1,245 + 3,439
Looking for compatible numbers, and taking advantage of the associative and commutative
properties, can speed up addition. Adding 4 + 9 + 5 + 7 + 8 + 9 + 2 + 3 + 6 + 5 + 1 just as
written could be tedious. But if you look for compatible numbers and rearrange, it’s not too bad.If you use these tactics on each place value column, even long addition problems can go quickly.
Take a look at the following addition problem.In the ones column, you can find 2 + 8 and 1 + 9 and another 5 to make 25. Put down the 5 and
carry the 2. In the tens, there’s a 3 + 7 and an 8 + 2 (that you carried) and another 9 for 29. Put
down the 9 and carry the 2. In the hundreds, you’ll find 7 + 3, 4 + 6 and 8 + 2 for a total of 30.
Put down the 0 and carry 3. There are two pairs that make 10 in the thousands, plus another 9,
and the ten-thousands will add to 16.49578923651
46915573829
10 10 10 10++++++++++
=++++++++++
=++++++
=10 9
5947,732
18,481
6,809
14,678
81,395+47,732
18,481
6,809
14,678
81,395
169,09523 22