Variables
 

Scales idea developed further

In the left hand pan of a scales are three packets of sweets, all exactly the same weight. In the right hand pan is a 12gm weight balancing the packets. What weight is in each packet?

Children should be trained to record their findings clearly step by step. They may gradually be led to use a letter for the unknown number that goes in the frame.

Let the unknown weight be x grams. (x is a placeholder for a number.)

x + 4 = 9 implies x = 5.

The weight is 5 grams

We check by putting 5 instead of x in the equation i.e. 5 + 4 = 9.

In the second example:

Let x be the number of grams in each packet of sweets. The two sides of the scales balance, and so we may write:

3x = 12 Divide each side by 3 x = 4.
Check: 4 + 4 + 4 = 12