Formula for percentage
The formula for percentage is the following and it should be easy to use if you follow the straightforward directions given. Study the formula below carefully before looking at the examples.
We will take some examples to illustrate. Let us start with the formula on the left.
An important thing to remember is to crossmultiply after you have identified the different parts of the formula.
Crossmultiply means to multiply the numerator of one fraction by the denominator of the other fraction.
How to use the formula for percentage on the left.
Example #1:
25 % of 200 is ____
In this problem,
of = 200,
is = ?, and
% = 25
We get:
is/200 = 25/100
Since
is in an unknown, you can replace it by y to make the problem more familiar.
y/200 = 25/100
Cross multiply to get y × 100 = 200 × 25
y × 100 = 5000
Divide 5000 by 100 to get y
Since 5000/100 = 50, y = 50
So, 25 % of 200 is 50
Example #2:
What number is 2% of 50 ?
This is just another way of saying 2% of 50 is ___
So, set up the proportion as example #1:
is/50 = 2/100
Replace is by y and cross multiply to get:
y × 100 = 50 × 2
y × 100 = 100
Since 1 × 100 = 100, y = 1
Therefore, 1 is 2 % of 50
Example #3:
24% of ___ is 36
This time, notice that
is = 36, but
of is missing
After you set up the formula, you get:
36/
of = 24/100
Replace of by y and cross multiply to get:
36/y = 24/100
y × 24 = 36 × 100
y × 24 = 3600
Divide 3600 by 24 to get y
3600/24 = 150, y = 150
Therefore, 24 % of 150 is 36
How to use the other formula for percentage on the right.
Now, we will take examples to illustrate how to use the formula for percentage on the right
Example #4:
To use the other formula that says part and whole, just remember the following:
 The number after of is always the whole.
 The number after is is always the part.
If a problem says 25 % of ___ is 60, then, we know that the whole is missing and the part = 60
Your proportion will like this:
60/
whole = 25/100
After cross multiplying, we get:
whole × 25 = 60 × 100
whole × 25 = 6000
Divide 6000 by 25 to get whole
6000/25 = 240, so whole = 240
Therefore, 25 % of 240 is 60
Example #5:
___% of 45 is 9
Here whole = 45 and part = 9, but
% is missing
We get:
9/45 =
%/100
Replacing % by x and cross multiplying gives:
9 × 100 = 45 × x
900 = 45 × x
Divide 900 by 45 to get x
900/45 = 20, so x = 20
Here we go! I hope the formula for percentage was helpful.

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