Math Core

Sometimes a story has three groups to put together. You can add three numbers the same way you add two: just one step at a time.

Two at a time

To add $3 + 4 + 2$ , add two numbers first. Then add the third.

$3 + 4 = 7$ , then $7 + 2 = 9$ .

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Here is a big secret: you can add the numbers in any order. The total stays the same. So look for a pair that is easy to add first.

Any order works

When you add three numbers, you can add any two first. The total does not change.

Look for a pair that makes ten or a double. Add that pair first.

Worked example: Make a ten first

Find $6 + 5 + 4$ .

$6 + 4$ makes ten! Add those first: $6 + 4 = 10$ . Then $10 + 5 = 15$ .

So $6 + 5 + 4 = 15$ .

Worked example: Use a double

Find $7 + 2 + 7$ .

$7 + 7$ is a double: $7 + 7 = 14$ . Then $14 + 2 = 16$ .

So $7 + 2 + 7 = 16$ .

Worked example: A three-part story

Kai picks 3 red flowers, 8 yellow flowers and 7 white flowers. How many flowers does he pick in all?

Add all three parts: $3 + 8 + 7$ . Look for a ten: $3 + 7 = 10$ . Then $10 + 8 = 18$ . Kai picks 18 flowers.

Common mistake

Don't forget a number! After you add the first two, check that you still add the third one. Cross off each number as you use it.

Practice 1

Find $2 + 3 + 4$ .

Type a number.

Practice 2

Find $8 + 4 + 2$ .

Type a number.

Practice 3

Find $5 + 3 + 5$ .

Type a number.

Practice 4

Amy has 4 red balls, 2 blue balls and 4 green balls. How many balls does she have in all?

Type a number.

Practice 5

Which pair is best to add first in $9 + 6 + 1$ ?

Practice 6

A bird house has 7 blue birds, 3 brown birds and 7 red birds. How many birds are there?

Type a number.

Practice 7

Jin scored 6 points, then 9 points, then 4 points. How many points did he score in all?

Type a number.