You have the right formula, but getting a true understanding of it can happen only if you work it through a few times. Ready?
The terms percentage rise, percentage difference, and percentage change all mean the same as percent change. To find percent change (increase or decrease), use this formula:
percent change = amount of change original amount
To work through this formula, you take three simple steps:
1. Figure out the number or amount by which the thing has changed (increased or decreased).
For example, if you won 25 games of chess against your brother last month and 30 games this month, the number increase is 5. Make that number the numerator (the top number) of the fraction:
2. Find the original amount.
The original amount is the number you started out with before you increased or decreased. If you won 25 chess games last month and won 30 games this month, the original amount is 25. Make that number the denominator (the bottom number) of the fraction. You now have a fraction:
3. Turn your fraction into a decimal and multiply by 100 to make it a percentage:
5 = 1 = 0.2 25 5
0.2 X 100 = 20%
So, you had a 20% increase in the number of games won, and you can now crown yourself Chess Champion of the House!
Forget how to convert a fraction to a decimal? Just divide the numerator of the fraction by the denominator. For example, convert 3/8 to a decimal:
3/8 is the same as 3 divided by 8 — now do the long division:
0.375 8)3.000 - 24 60 - 56 40 - 40 0
So, 3/8 = 0.375.
To change this to a percentage, multiply by 100 to get 37.5%.