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Door 7 · Grade 1

- Basic Subtraction

Take away numbers, take down monsters!

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What is Subtraction?

Subtraction means TAKING AWAY.
The symbol is - (minus). The answer is called the DIFFERENCE.
You have 5 sweets and eat 2: 5 - 2 = 3 sweets left.

Worked example

Problem: Take away: 7 - 3 = ?

  1. Start with 7 objects: O O O O O O O
  2. Cross out 3: X X X O O O O
  3. 4 are left.

Answer: 4

Subtracting on a Number Line

Start at the first number.
Jump BACKWARD as many steps as the number you take away.
To do 9 - 4: start at 9, jump back 4: 8, 7, 6, 5. So 9 - 4 = 5.

Worked example

Problem: Use the number line: 8 - 3 = ?

  1. Start at 8.
  2. Jump back 3 steps: 7, 6, 5.
  3. You land on 5.

Answer: 5

Subtraction Within 20

Finding the DIFFERENCE tells how many more one group has.
12 - 5: count back 5 from 12: 11, 10, 9, 8, 7. Answer 7.
Subtracting 0 changes nothing: 15 - 0 = 15.
A number minus itself is 0: 8 - 8 = 0.

Worked example

Problem: Subtract: 14 - 6 = ?

  1. Count back 6 from 14: 13, 12, 11, 10, 9, 8.
  2. The answer is 8.

Answer: 8

Two-Digit Subtraction (No Regrouping)

Subtract the ONES first, then the TENS.
38 - 15: ones are 8 - 5 = 3, tens are 3 - 1 = 2. Answer 23.
47 - 4: ones are 7 - 4 = 3, tens stay 4. Answer 43.

Worked example

Problem: Subtract: 56 - 24 = ?

  1. Ones: 6 - 4 = 2.
  2. Tens: 5 - 2 = 3.
  3. Answer: 32.

Answer: 32