Year 3 Informal and mental strategies for adding and subtracting two 3-digit numbers worksheet

“Adding by splitting numbers” is free to print, with no account. It is the first sheet in the Year 3 maths unit “Informal and mental strategies for adding and subtracting two 3-digit numbers”, for children aged 7 to 8, and takes about 20 minutes.

Print it on A4. The child's pages come first; the answers, and what each wrong answer tells you, are on the grown-up page that follows. Weeks 14 to 16 of the year, 10 sheets in the unit.

Free sample · answers on the last page

Adding by splitting numbers

Name: ____________ · Date: ____________
Year 3 · Maths · about 20 minutes
Answers are on the grown-up page

Today I can add two 3-digit numbers by splitting them into hundreds, tens and ones.

A Look back3 min

1.
6 tens is
2.
300 + 40 =
3.
470 407

B Watch me, then you4 min

Add 232 and 146 by splitting each number into hundreds, tens and ones.

Watch me

232 is 200, 30 and 2. 146 is 100, 40 and 6.

Add the hundreds, then the tens, then the ones: 300, 70 and 8.

300 + 70 + 8 = 378.

Now you

1.
312 + 245 =

C Your turn6 min

Split each number, then add the groups.

1.
300 + 200 =
2.
320 + 200 =
3.
320 + 240 =
4.
325 + 240 =

Say it out loud: What changed from one row to the next, and what did you add because of it?

D Spot the mistake3 min

Ravi says: “30 tens and 40 tens make 70, so the answer is 70.”

1.
How many is 30 tens and 40 tens altogether?

E Think deeper4 min

Partitioning helps you check an answer.

1.
The whole is 600. Write two 3-digit numbers that add to 600. Then explain how splitting them into hundreds, tens and ones shows it is right.

How did it feel?

I can do it Nearly Not yet

For the grown-up

Adding by splitting numbers · 2 minutes to read

Answers, and what a wrong one tells you

A

1. 60

2. 340

3. >

B

1. 557 If your child writes 512, the tens digits were added as 1 + 4 = 5 and not as 10 + 40 = 50. Write the tens as tens, then add.

C

1. 500

2. 520

3. 560 If your child writes 500, only the hundreds were added. Add the tens next: 20 and 40 make 60.

4. 565 If your child writes 560, the 5 ones were left out. Add them at the end: 560 + 5 = 565.

D

1. 700. 30 tens + 40 tens = 70 tens, and 70 tens is 700. If your child writes 70, the tens were added but not converted. Ask how many hundreds 70 tens makes.

E

1. Look for: two 3-digit numbers whose sum is 600, with an explanation using hundreds, tens and ones

Words to use

Say“Split each number first, then add the hundreds, the tens and the ones.”

Instead of“Just line the numbers up and tell them the answer.”

After the sheet

Use coins: pound coins stand for hundreds, 10p coins for tens and 1p coins for ones. Make two amounts with coins, then count each kind and add them together.

Tick what your child got right in StudyDen. Anything missed comes back in a later Look back box, so there's no need to redo the sheet.

The rest of this unit

9 more sheets come with a StudyDen plan, in teaching order:

Adjust, then fix it(with a plan)
Moving numbers to add(with a plan)
Pick the quickest way(with a plan)
Subtract by bridging ten(with a plan)
Finding the gap(with a plan)
Finding the gap(with a plan)
Pick the quickest route(with a plan)
Reading charts and tables(with a plan)
Number Stories with Hundreds(with a plan)

Every Year 3 maths worksheet

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