Balance Scale Unknowns
Finding the missing weight on a simple market scale.
Keep both sides equal while finding the unknown.
A scale balances when 7 known blocks and one mystery bag weigh the same as 12 blocks. Find the mystery weight.
Balance Scale Unknowns illustration
Finding the missing weight on a simple market scale.
Solve 7 + box = 12.
- Both sides balance at 12. The known 7 blocks are already on the left side.
- Count how many more blocks are needed to reach 12. The mystery box is 5.
Struggle support
Rescue lab
Mystery bag on the scale
A market scale balances with seven known blocks and one covered bag on one side, and twelve blocks on the other side.
Draw two scale pans with matching total height, then hide the unknown bag.
Put 7 counters beside a covered cup and 12 counters on the other side.
Both sides must stay equal because the scale balances.
Match the 7 known counters, then count the unmatched counters.
The right side has 5 counters not yet matched.
Write the missing amount in place of the box.
7 + box = 12, so box = 5.
Treating the box as a decoration instead of a number.
Ask what the covered bag must weigh for the scale to balance.
Say the box means an unknown number that makes the sentence true.
Using the same operation without undoing the action.
Ask what operation would remove the known 7 from both sides.
Undo addition with subtraction or count up from 7 to 12.
Say what the unknown stands for before solving, then check it in the original equation.