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How to add and subtract in your head | Year 4 Mathematics PDF Download

Rounding numbers

Rounding numbers can simplify addition by adjusting numbers to the nearest multiple of 10 or 100.
Here are some examples:

  • When adding 9 to a number:
    • Step 1: Add 10 to the number.
    • Step 2: Subtract 1 from the result to adjust back.
    • Example: 36 + 9 = 36 + 10 - 1 = 45
  • When adding 18 to a number:
    • Step 1: Add 20 to the number.
    • Step 2: Subtract 2 from the result to get the final sum.
    • Example: 48 + 18 = 48 + 20 - 2 = 66
  • When adding 97 to a number:
    • Step 1: Add 100 to the number.
    • Step 2: Subtract 3 to adjust and find the sum.
    • Example: 439 + 97 = 439 + 100 - 3 = 536
  • When adding 0.9 to a number:
    • Step 1: Add 1 to the number.
    • Step 2: Subtract 0.1 from the result to get the final sum.
    • Example: 3.7 + 0.9 = 3.7 + 1 - 0.1 = 4.6

Breaking Down Numbers

Breaking down numbers can be a useful strategy to mentally add or subtract numbers.
For instance, let's consider finding the difference between 38 and 63:

  • Start by counting from 38 to 40, keeping the difference of 2 in mind.
  • Next, count from 40 to 60, which is a difference of 20.
  • Finally, count from 60 to 63, which is a difference of 3.
  • Add these differences together: 2 + 20 + 3 = 25.

Question for How to add and subtract in your head
Try yourself:
What is a helpful strategy to mentally add or subtract numbers by breaking them down into smaller parts?
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FAQs on How to add and subtract in your head - Year 4 Mathematics

1. How can I improve my mental math skills for adding and subtracting numbers in my head?
Ans. One way to improve your mental math skills for adding and subtracting numbers is to practice regularly. You can start by doing simple calculations in your head and gradually increase the difficulty level. Additionally, using number bonds or breaking numbers down into smaller, more manageable parts can also help improve your mental math abilities.
2. Are there any mental math techniques that can make adding and subtracting easier?
Ans. Yes, there are several mental math techniques that can make adding and subtracting numbers easier. These include using the commutative property (changing the order of numbers being added or subtracted), using the associative property (grouping numbers in different ways), and using shortcuts like rounding numbers to the nearest ten or hundred.
3. How can I quickly add or subtract large numbers in my head without using a calculator?
Ans. One way to quickly add or subtract large numbers in your head is to break the numbers down into smaller, more manageable parts. For addition, you can add the tens and then the ones separately before combining the results. For subtraction, you can use the borrowing technique or break down the numbers into more easily subtracted parts.
4. What are some tips for maintaining accuracy when adding and subtracting in your head?
Ans. To maintain accuracy when adding and subtracting in your head, it is important to double-check your work and practice regularly to improve your mental math skills. You can also use estimation techniques to quickly check if your answer is reasonable before moving on to the next calculation.
5. How can I teach children to add and subtract in their heads effectively?
Ans. To teach children to add and subtract in their heads effectively, you can use visual aids like number lines or manipulatives to help them understand the concept of addition and subtraction. Encouraging them to practice mental math regularly and providing positive reinforcement can also help improve their skills.
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