# Direct Proportion

If two quantities a and b are related in such a way that an increase or decrease in b results in a proportionate increase or decrease in a, then a and b are said to be directly related or in direct proportion.

This is expressed as(a is directly proportional to b).

When we can write a = bk, where k is a constant known as the constant of proportionality.

Example: The cost of travel increases when the price of fuel increases. Thus, cost of travel  price of fuel.