Direct and Inverse Proportion

There is usually at least one question on the math section which requires the student to know either direct proportion or inverse proportion. Quite simply with direct proportion if x goes up y goes up in proportion. If x decreases, y decreases in proportion. Here is a helpful rule for Direct proportion using variables x and y can be thought of as y=xk where k is a constant. Cross multiply and you get a variation of this equation: y/x=k. For example if x=2 when y=4, then when x=4 then y=8. The constant k=2 so y will always be twice x. Simple enough? If x were to be reduced from 2 to 1 then y would still be twice x but in this case it would be reduced to 2. In our next entry the more difficult concept of inverse proportion will be tackled.