Percent Differential:

Percent differentials are used to give a means of comparing changes within quantities or amounts. A Percent differential express the relationship among some initial condition and another specified condition.

The technique of calculating percent differential involves the subsequent:

Step 1:  Subtract the original value from the present value.

Step 2:  Divide by the original value.

Step 3:  Multiply by 100.

Step 4:  Add the percent symbol (%).

Example:

A tank initially contains 50 gallons of water.   Five gallons are drained out.   Through what percent is the amount of water in the tank decreased?

Solution:

Step 1: The difference among initial and final is given in the problem:  5 gallons.

Step 2: 5/50 = 0.1

Step 3: 0.1 x 100 = 10% Five gallons represents 10% of the original 50 gals that were in the tank.