Look at the two pans of the balance. On the left is a mystery bag holding x counters, along with 4 loose counters. On the right are 9 counters. The beam is level, so both sides weigh exactly the same.

How many counters are hiding in the bag?

Look at three balanced equations on the scales. Each one has a mystery bag on it. Notice how each bag ends up alone on its side.

The next bag is drawn short: 3 counters have already been taken out of it. On the scales those 3 are put back on both pans. Filling the bag up again is how we undo a take-away, so a minus in the equation is undone by adding back.

This last one has three bags together. The pans are shared into three equal groups.

We solve three on the scales together: first x + 6 = 10, then x − 2 = 5, then 4x = 12. Remember the take-away one: the bag has already lost 2, so we add 2 back to both pans. For each one the whole class names the move out loud together, then one pupil at the board slides the bag's value until the beam sits level and presses Check.

We work through these on the scales: x + 7 = 12, then 4x = 24, then x − 9 = 6, then 3x = 9. For each one, name the move, slide the bag's value, and press Check.