This answer is really backwards for both changes. Remember that in a direct proportion, such as volume/temperature, when one of the values is increased, the other value must be also increased by the same amount. Think of a normal fraction 1/2 = 0.5. If you increase the 1 to 2 then the 2 must be increased to 4 to maintain the value of 0.5. If you use this simple example as a memory tool, direct proportions are easy.

An indirect proportion, such as pressure x volume, is just the opposite. When one of the values is increased, the other value must be decreased to keep the product of the two values the same. Think of the example 3 x 4 = 12. If you increase the 3 to 6, what do you have to do to the 4 to make the product still equal to 12? You have to change the 4 to 2. You doubled the 3 to make 6 and so you must multiply the 4 by 1/2.