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Door 10 · Grade 1

= Algebraic Thinking

Balance the equation, find the hidden number!

▶ Play Door 10

The Equal Sign

The = sign means BOTH SIDES ARE THE SAME.
3 + 2 = 5 means 3 + 2 and 5 are equal amounts.
It is like a balance scale: both sides must weigh the same!

Worked example

Problem: Is this true or false: 4 + 1 = 5? (type true or false)

  1. Left side: 4 + 1 = 5.
  2. Right side: 5.
  3. Both sides are the same, so it is TRUE.

Answer: true

Missing Number Problems

A missing number hides in the equation.
3 + ? = 7. Think: 3 plus what makes 7? The answer is 4.
? - 2 = 6. Think: what take away 2 leaves 6? The answer is 8.

Worked example

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

  1. 5 plus what makes 9?
  2. Count from 5 to 9: 6, 7, 8, 9. That is 4 jumps.

Answer: 4

Balancing Equations

Both sides of = must balance.
2 + 3 = 4 + ? Left side is 5, so the right side needs 1 (4 + 1 = 5).
Always make both sides equal!

Worked example

Problem: Balance it: 6 + 2 = 5 + ?

  1. Left side: 6 + 2 = 8.
  2. 5 plus what makes 8?
  3. 5 + 3 = 8.

Answer: 3