**Weighing scales **

Pupils may at first find the solution of simple (lst. degree) equations by intuition, as they have been doing in previous classes. They now need to learn how to solve them by applying a few fundamental principles, which are best introduced with the aid of weighing scales. The pupils will have established in previous classes that the scales balance because the same weight is in each pan:

What other weight must be in the left pan with the 4 gm weight so that they will balance the 10 gm. weight in the right pan? If we take the 4 gm weight from the left pan, what must we take from the right pan to restore the balance that has been destroyed?

? + 4 = 10

? + 4 – 4 = 10 – 4

? = 6

so that 6 is the number for the frame.