Proportionality formulae

Direct proportion

• These all mean the same thing
  • y is directly proportional to x
  • y varies directly with x
  • y ox x
  • y=kx

Inverse proportion

• These all mean the same thing
  • y is inversely proportional to x
  • y varies inversely with x
  • y ox 1/x
  • y = k/x

Working it out

• You can find a proportionality formula if you know the type of proportionality and are given two corresponding values for the variables. Follow these steps
  • Write down the formulae using k for the constant of proportionality
  • Substitute the values of v and t you are given
  • Solve the equation to find the value of k
  • Write down the formula putting in the value of k
  • Once you have written your formula, you can use it to find the value of one variable if you know the value of the other