Unknowns and balances
Strategy card
An equation is a balance: both sides stay equal.
- Step 1: Find the unknown (the box or letter).
- Step 2: Undo the operations in reverse order.
- Step 3: Do the same thing to both sides.
- Step 4: Check by putting your answer back in.
Tip: Substitute your answer back in. It's the quickest check.
Worked example
Use the rule. What is the answer?
a ◆ b means 5 × a + b
2 ◆ 1 = ?
- A: 11 (the answer)
- B: 8
- C: 7
- D: 14
- E: 13
Why: Put the numbers in: 5 × 2 + 1 = 11.
Your turn
Your turn 1 of 3
Use the rule. What is the answer?
a ◆ b means 4 × a + b
2 ◆ 5 = ?
Your turn 2 of 3
What number goes in the box?
5 × □ + 9 = 44
Your turn 3 of 3
Use the rule. What is the answer?
a ◆ b means 4 × a + b
4 ◆ 3 = ?
Keep practicing
Grown-ups: Ask: "What would you do to undo that?" Parent guide
Next lesson: Arguments and evidence