How do you do percentage increase in math?

Answer 1

There are two ways. Suppose you want to increase a number X by Y%:

The simple way (with limited applications).

• Calculate Y% of X = X*Y/100
  
• Add this X.

The less simple way but one with applications for the next steps in percentage changes (compound changes and, if given the value AFTER a percentage increase, finding the original value:

• Calculate the multiplier, M = 1 + Y/100
  
• Multiply X by M.

The advantage of using M are:

If you need to calculate the value of X if it increases by Y% every year for n years, the answer is

X*M^n

If you know that AFTER an increase of Y% the value was X, then the original value was X/M.

Of course, if it is a Y% decrease, then M = 1 - Y/100.