Proportions are equivalent ratios.
If two things are increasing by the same rate, they are proportional.

3 characteristics of a proportional relationship:
  • ratios are equivalent: 1/2 = 4/8 = 6/12
  • graph goes through the origin [(0,0) must be part of the data]
  • equation does not have a constant: y=2x NOT y=2x+3 (the +3 makes it non proportional)