by Jason Marshall

## How to Do It

### But that’s a lot to keep track of. Remember the commutative property of addition? You don't have to add these numbers in the order they're given to you. Instead, if you start by pairing up numbers that add to ten—in this case 3 and 7, and 9 and 1—that leaves you with an easy problem. You just have to add the two 10s to the remaining number 5 that didn’t pair with anything:  10 + 10 + 5 = 25

When adding a list of numbers, look for pairs or groups of numbers that add to ten.

## Wrap Up

### You can find several practice problems below to help you sharpen your skills. Remember, try to work them out in your head if you can. Next week we'll combine these two tips with a couple of other tricks, and continue your transformation into a calculating machine. Then, get ready, because the week after that we’re going to begin our foray into the world of fractions, decimals, and percentages.

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Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Submit your questions to mathdude@quickanddirtytips.com, the aforementioned Facebook page, or on Twitter. Thanks for reading, math fans!

Practice Problems

The only way to become proficient is to practice! For these problems, add from the top down. Be sure to look for pairs or groups of numbers that add to ten. For example, in this problem

3

6

4

9

+ 1

you should count in your head: 3, 13, 23. In other words, 3 + (6+4) + (9+1). Here are two practice problems with a single column of numbers to add:

Problem #1:

7

8

5

2

+ 3

Problem #2:

4

3

2

8

+ 1

Here’s a problem with two columns of numbers to add. Look for pairs that add to ten in each column.

Problem #3:

82

18

57

31

+ 73

You can find the answers to all the practice problems on the Math Dude’s Facebook page