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Door 8 · Grade 1

-* Subtraction Strategies

Ninja tricks for lightning subtraction!

▶ Play Door 8

Counting Backward

For small take-aways, count backward.
11 - 3: say 11, then count back 10, 9, 8. Answer 8.
Use your fingers to keep track of the jumps!

Worked example

Problem: Count backward: 13 - 4 = ?

  1. Start at 13.
  2. Count back 4: 12, 11, 10, 9.

Answer: 9

Using Addition Facts

Addition and subtraction are best friends!
If 6 + 4 = 10, then 10 - 4 = 6 and 10 - 6 = 4.
To solve 15 - 8, think: 8 + ? = 15. The answer is 7.

Worked example

Problem: Use addition: 14 - 9 = ?

  1. Think: 9 + ? = 14.
  2. 9 + 5 = 14.
  3. So 14 - 9 = 5.

Answer: 5

Missing Numbers and Real Life

Sometimes a number is hiding: 7 - ? = 3.
Think: 7 take away WHAT leaves 3? The answer is 4.
Real life: had 10 rupees, spent some, 6 left. You spent 4!

Worked example

Problem: Find the missing number: 9 - ? = 5

  1. 9 take away what leaves 5?
  2. 9 - 4 = 5, so the missing number is 4.

Answer: 4