Percentage calculator
Calculator finds solutions to common percentage problems. It's done in easy way: more like stories and everyday situations, less like math language.

# 1. Basics:

1.1.
% is equal to
0.5
or
 50 100
.
1.2. The number
is equal to
19
%.
1.3. The fraction
is equal to
75
%.
1.4.
% from the number
is
50
.

# Some facts#

• One percent (1%) is equal to fraction 1/100 or 0,01:
$1\ percent = 1\% = \dfrac{1}{100} = 0,01$
• To convert some number into percent, you need to convert it to fraction with 100 denominator first. Then, nominator of fraction will tell you "number of percents".
ⓘ Example: Fraction 3/4 is equal to 75%, because after converting it to denominator 100 we get:
$\dfrac{3}{4} = \dfrac{3 \times 25}{4 \times 25} = \dfrac{75}{100} = 75\%$
• If you need to calculate a percent of a number, you have to multiply that number by a proper fraction with 100 denominator.
ⓘ Example: 50% from number 10 is equal to 5, because:
$50\% \times 10 = \dfrac{50}{100} \times 10 = \dfrac{50 \times 10}{100} = \dfrac{5\cancel{00}}{1\cancel{00}} = 5$
• The concept of percentage is very useful and popular in many areas of our life, for example:
• Income from bank deposit is usually defined as percent of capital, that you would earn after one year. It's so called annual rate of return.
• Change in a value is often expressed as percentage of inital value. For example: the handbag is 20% cheaper than it was before the summer discount.
• Concentration of one substance in another is often expressed in percentage values (percentage concentration). For example you can buy 3% solution of hydrogen peroxide (H2O2) to desinfect wounds. It means that in 100g of solution you'll get 3g of the active substance (i.e. hydrogen peroxide).

# Tips & tricks#

• Use percentage commutativity and surprise your friends!
• ⓘ Example: Let's calculate 18% from 50 in memory. Looks difficult? Don't worry - there is nothing easier. Let's swap number and percentage and we get 50% from 18. 50% of something is same as half of something ! So, we need half of 18, which is 9.
$18\% \times 50 = 50\% \times 18\% = \dfrac{1}{2} \times 18 = 9$
• Why does it work? Percentage commutativity is related to multiplication commutativity. Because calculating percentage from given number is the same as multiplying this number by fraction (x/100), this operation is commutative too.
• ⓘ Hint: Remember and impress friends: X% from number Y is the same as Y% from number X.
$X\% \times Y = Y\% \times X$

# How to use this tool#

• First of all, find the sentence in calculator, which describes your problem in the closest way. However, don't take those sentences too literally ! Those sentences describe example situations - like buying handbag under promotion. However, you can enter any other product in this place. Be creative, don't waste your imagination.
• Next, click on one of input fields in the sentence and enter your own value.
• After you've entered the numbers in the particular sentence, the other part of a sentence will adjust automatically, displaying the correct number as a solution.
• Remember - if you can't find a sentence describing your situation, feel free to drop us a word. We will be happy to add the missing case for you!

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