I understand the formula for percentage change is:
end value - start value/ start value = x% or percentage change.
and percentage of is
x * x%/100 = z
10 x 100/100 = 10%
however you can use percentage of to calculate percentage change, like this:
60-50/50 * 100 = 20%
Using percentage of:
50 x y% = 60
y = 60/50*100 = 120
I can't seem to understand why you would use one over the other, when you can get the same result using either.
When a value increases/decreases and you know both the original and the final values, you find the percentage change.
Say your score was 500 and now it is 600. The percentage change is (600 - 500)/500 * 100 = 20%
'percentage of' is used in many situations e.g. You might have the initial value and percentage increase/decrease. You need to find the final value.
Your GMAT score has increased by 20%. Your first GMAT score was 500. What is the 20% of 500?
(20/100) * 500 = 100
So your new GMAT score must be 500 + 100 = 600 (final value)
Another example for 'percentage of'
There are total 120 students in a class. Out of these, 48 are boys. What 'percentage of' students are boys?
We need to find this - 48 is what percentage of 120? Say 48 is x% of 120.
120 * x/100 = 48
x = 40%
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