Two quantities are said to be in direct proportion if they increase or decrease in the same ratio. If two amounts are directly proportional we can scale the quantities up by multiplying. 150 ml × 5 = ...

There is a direct proportion between two values when one is a multiple of the other. For example, \(1\text{cm} = 10\text{mm}.\) To convert \(\text{cm}\) to \(\text{mm}\), the multiplier is always 10.