Direct proportion is a relationship between two values where they both increase or decrease at the same rate. In other words, if one value doubles, the other one will also double, and if one is reduced by half, the other follows. This happens when the ratio between the two values stays constant.
For example, if you are buying apples and each apple costs 50 pence, the total cost is directly proportional to the number of apples you buy. If you buy 1 apple, it costs 50 pence; if you buy 2 apples, they cost 100 pence, and so on. In a graph of direct proportion, the line will always pass through the origin (0,0) and be straight, showing the constant rate of change.
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