➕ Addition up to 999

What your child will learn

• Students will be able to add two three-digit numbers without regrouping using blocks, expanded form and the column method.
• Students will be able to add with regrouping of ones into tens, and explain the carried 1 as one ten.
• Students will be able to add with regrouping of tens into hundreds, including regrouping in both columns, with sums up to 999.
• Students will be able to add mentally using friendly strategies: making tens, adding hundreds first, and adding near-multiples of 10 and 100.
• Students will be able to estimate a sum by rounding to the nearest ten and use it to judge whether an exact answer is reasonable.
• Students will be able to solve one-step and simple two-step word problems that need addition, choosing addition from the story words.

Lessons in this unit

1. Adding without regrouping: Add two three-digit numbers where no column goes past 9, first by combining blocks and expanded form, then in columns (ones first).
2. Carrying from ones to tens: Add when the ones column makes 10 or more: exchange 10 ones for 1 ten with blocks, then record the carried 1 above the tens column.
3. Carrying from tens to hundreds: Add when the tens column makes 10 or more tens, exchanging 10 tens for 1 hundred, including sums that carry in both columns. Keep every sum at or below 999.
4. Adding in your head: Add without columns using friendly strategies: add hundreds and tens first, make the next ten, and use near numbers like 199 → 200.
5. Estimating sums: Round each number to the nearest ten, add the rounded numbers to get an 'about' answer, and use it to check whether an exact sum is reasonable.
6. Story sums with addition: Read a story, find the numbers and the clue words (altogether, in all, total, more), decide that it is addition, write the sum, solve it and answer in a sentence. Include one simple two-step problem.

Key words

sum

The answer when we add.

regroup / carry over

Change 10 ones into 1 ten (or 10 tens into 1 hundred) and move it to the next column.

column method

Writing numbers one under the other with ones under ones, tens under tens.

estimate

A quick 'about' answer before working it out exactly.

altogether / in all / total

Words in a story that tell us to add.

Help your child at home

What to watch for

Numbers are lined up from the left: 342 + 15 becomes 342 + 150.

Help: Line up ones under ones. Use the H T O chart so 15 sits in the T and O columns only.

Write the whole 13 in the ones column: 348 + 225 = 5613.

Help: 13 ones is 1 ten and 3 ones. Only one digit fits in a column. Move the ten to the tens column.

Carry the 1 to the wrong column or add it twice.

Help: Cross out each carry after you use it. One carry, one use.

199 + 45 = 245 because 200 + 45 = 245 (forgetting to take the 1 back).

Help: We added 1 extra to make 200, so we must take 1 away at the end: 245 − 1 = 244.

Try this at home

• 342 + 215: blocks for each number, then 300 + 200, 40 + 10, 2 + 5, then the same sum in columns ones first
• 348 + 225 with blocks, exchange, then columns
• 372 + 254 with the tens exchange
• 320 + 400 on a number line in hundreds

Quick questions to ask aloud

1. Add: 342 + 215
   Show answer

   Ones: 2 + 5 = 7. Tens: 4 + 1 = 5. Hundreds: 3 + 2 = 5. The sum is 557.
2. Add: 348 + 225
   Show answer

   Ones: 8 + 5 = 13 → write 3, carry 1 ten. Tens: 4 + 2 + 1 = 7. Hundreds: 3 + 2 = 5. The sum is 573.
3. Add: 372 + 254
   Show answer

   Ones: 2 + 4 = 6. Tens: 7 + 5 = 12 tens → write 2, carry 1 hundred. Hundreds: 3 + 2 + 1 = 6. The sum is 626.

Parent guide: how to help your child with Class 3 Maths

Frequently asked questions

What will my child learn in "Addition up to 999" (Class 3 Maths)?

Your child will be able to: add two three-digit numbers without regrouping using blocks, expanded form and the column method.; add with regrouping of ones into tens, and explain the carried 1 as one ten.; add with regrouping of tens into hundreds, including regrouping in both columns, with sums up to 999.; add mentally using friendly strategies: making tens, adding hundreds first, and adding near-multiples of 10 and 100.; estimate a sum by rounding to the nearest ten and use it to judge whether an exact answer is reasonable.; solve one-step and simple two-step word problems that need addition, choosing addition from the story words..

How does MangoMindz teach "Addition up to 999"?

In 6 short parts (Adding without regrouping, Carrying from ones to tens, Carrying from tens to hundreds, Adding in your head, Estimating sums, Story sums with addition). Each part has a picture-based lesson read aloud by Mango Teacher, a quick check, and a quiz built from common mistakes children make, with Mango, a study buddy, for questions.

How long does "Addition up to 999" take?

About 160 minutes in total, spread over 6 parts of 15–25 minutes each.

How can I help my child with "Addition up to 999" at home?

Work through a small example together, such as: 342 + 215: blocks for each number, then 300 + 200, 40 + 10, 2 + 5, then the same sum in columns ones first; 348 + 225 with blocks, exchange, then columns. Then ask a quick question aloud: Add: 342 + 215

What mistakes do children often make in "Addition up to 999"?

Numbers are lined up from the left: 342 + 15 becomes 342 + 150. Fix: Line up ones under ones. Use the H T O chart so 15 sits in the T and O columns only. Write the whole 13 in the ones column: 348 + 225 = 5613. Fix: 13 ones is 1 ten and 3 ones. Only one digit fits in a column. Move the ten to the tens column. Carry the 1 to the wrong column or add it twice. Fix: Cross out each carry after you use it. One carry, one use.

Is "Addition up to 999" free on MangoMindz?

Yes. Every lesson part and quiz in "Addition up to 999" is free on MangoMindz, with no ads.