When you say "Percent" you are really saying "per 100"
And 25% means 25 per 100
Formula for percentage
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
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 #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
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
http://www.basic-mathematics.com/formula-for-percentage.html
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
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 #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
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
Percentage increase and decrease
Sometimes due to inconsistent usage, it is not always clear from the context what a percentage is relative to. When speaking of a "10% rise" or a "10% fall" in a quantity, the usual interpretation is that this is relative to the initial value of that quantity. For example, if an item is initially priced at $200 and the price rises 10% (an increase of $20), the new price will be $220. Note that this final price is 110% of the initial price (100% + 10% = 110%).
Some other examples of percent changes:
- An increase of 100% in a quantity means that the final amount is 200% of the initial amount (100% of initial + 100% of increase = 200% of initial); in other words, the quantity has doubled.
- An increase of 800% means the final amount is 9 times the original (100% + 800% = 900% = 9 times as large).
- A decrease of 60% means the final amount is 40% of the original (100% − 60% = 40%).
- A decrease of 100% means the final amount is zero (100% − 100% = 0%).
(New Value / Old Value) * 100 = % Value
http://www.basic-mathematics.com/formula-for-percentage.html
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