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 it below carefully before looking at the examples
We will take examples to illustrate.Let us start with the formula on the left
An important thing to remember: Cross multiply
It means to multiply the numerator of one fraction by the denominator of the other fraction
Examples #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
Examples #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
Examples #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
Now, we will take examples to illustrate how to use the formula for percentage on the right
Examples #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 I say 25 % of___ is 60, we know that the whole is missing and part = 60
Your proportion will 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
Examples #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 these formula for percentage were helpful.