Mental addition and subtraction

Mental addition and subtraction: what children learn

In this game children match calculations such as 12,500 + 3,000 and 23,999 + 6,001 to their answers. They are chosen so that a mental method, not a written one, is the best choice.

Supports part of Common Core 4.NBT.B.4, practicing mental methods with large numbers alongside the standard algorithm. This focused game does not cover the entire standard.

Common Core connection: 4.NBT.B.4. This is focused practice for part of the standard.

How to play

Pick a card on the left, then the card on the right that matches it. Each game has 6 pairs. Wrong matches are counted as mistakes, and you get three stars for a game with no mistakes.

Step by step

1. Look for round numbers. 12,500 + 3,000 changes only the thousands digit: 15,500.
2. Make a number round. 23,999 + 6,001: move 1 from 6,001 to 23,999 to make 24,000 + 6,000.
3. Bridge through a multiple. 9,950 + 50: 50 more makes the next thousand, 10,000.
4. Subtract the round part. 61,200 − 1,200 = 60,000.

Worked examples

Common mistakes and how to fix them

• Reaching for a written method for every calculation. Look at the numbers first. Are any of them round?
• Changing the wrong digit. Say the place value of each digit: 3,000 means 3 thousands.
• Losing track when bridging. Write down the step you reached, such as 10,000.

Activities to try at home

• Ask quick mental questions in the car: 45,000 − 2,000?
• Use prices to practice: what is $9,950 + $50?
• Challenge each other to find the quickest way to work out a calculation.

Ideas for the classroom

• Students sort calculations into 'mental' and 'written' and explain why.
• Use a number line to show bridging through a multiple of 1,000.
• Students compare strategies for the same calculation.

Free printable game and worksheet

The free printable starts with a game sheet, such as a color-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.

Open the free printable game and worksheet

Frequently asked questions

Related topics

• Adding and subtracting large numbers (Grade 4 math) – Add and subtract 5- and 6-digit numbers with the column method. A free Grade 4 math game.
• Rounding numbers to 1,000,000 (Grade 4 math) – Round numbers up to 1,000,000 to the nearest 10, 100, 1,000, 10,000 or 100,000. Free Grade 4 math game.
• Multiplying and dividing by 10, 100 and 1,000 (Grade 5 math) – Multiply and divide whole numbers and decimals by 10, 100 and 1,000. Free Grade 5 math game.
• Column methods with 4 digits (Grade 4 math) – Add and subtract 4-digit numbers with the column method. A free Grade 4 math game.
• Missing numbers and inverse operations (Grade 4 math) – Use the inverse to find the missing number in □ + 2,350 = 5,000. A free Grade 4 math game.
• Column addition and subtraction (Grade 3 math) – Add and subtract 3-digit numbers with the column method, exchanging when you need to. A free Grade 3 math game.

Back to Grade 4 math