Algebra · Challenge 11 of 25 · about 5 min
Missing Number Balance
Keep both sides of an equation balanced to find a missing number.
Year 4 challenge progress
0 of 25 complete
1 Read
Your challenge
□ + 275 = 640. What number belongs in the box?
Take your time. Your answer is checked only when you choose Check Answer.
Curriculum details
- Curriculum code
- VC2M4A01
- Strand
- Algebra
- Focus
- Find an unknown value in an addition equation.
2–5 Notice · Build · Move · Connect
Interactive visual
An interactive Keep the balance equal model is ready. Choose Show Visual Trick to reveal and hear one mathematical change at a time.
Visual Trick
Keep the balance equal
What you remove from one side must also be removed from the other side.
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Step 1
Balance an unknown box and 275 against 640.
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Step 2
Remove 275 from both sides.
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Step 3
Count up from 275 to 300, 600 and 640.
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Step 4
Add the jumps 25 + 300 + 40 to reveal the unknown amount.
6 Solve
Your answer
7 Check
Worked explanation
Why the answer makes sense
- Subtract the same 275 from both sides of the equation.
- 640 − 275 = 365.
- Check: 365 + 275 = 640, so the balance stays equal.
Challenge complete
This counts as one completed curriculum item. You can replay the model or review it again anytime.