# 1. Basics:

1.1. % is equal to 0.5
| |||

1.2. The number is equal to 19 | |||

1.3. The fraction 75 | |||

1.4. % from the number is 50 |

# 2. Shopping:

2.1. The bike was at a price of $. Next, its price has been raised by %. After that, the bike costs 525 $ |

2.2. I'm a regular customer in The Shop and I obtained % discount for future shopping. Regular price of washing machine is $, but I will pay only 800 $ |

2.3. Yeah! There is a promotion this week - it's % discount for all products. Some nice handbag costs $ now. It means, the same handbag was at a price of 58.82 $ (58 $ and 82 cents) |

2.4. The mobile phone costs $ in first shop and $ in another one. It means that, price offered by second shop is 20% higher |

# 3. Bills:

3.1. My usual electricity bill is about $ per month. Unfortunately, the bald man in TV was talking about upcoming increase of electricity price by %. It means I will pay 151.5 $ (151 $ and 50 cents)1.5 $ (1 $ and 50 cents) |

3.2. The landlord increased my rent by $. Before that, I was paying $ to him. This means my rent has grown by 22.22 |

3.3. My monthly gas bill is $ in average. It turned out, that I would pay $ when I switch to another supplier. It will be 20% less |

# 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 (H
_{2}O_{2}) to desinfect wounds. It means that in 100g of solution you'll get 3g of the active substance (i.e. hydrogen peroxide).

- Income from bank deposit is usually defined as percent of capital, that you would earn after one year. It's so called

# 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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# Ancient version of this site - links

In December 2016 the Calculla website has been republished using new technologies and all calculators have been rewritten. Old version of the Calculla is still available through this link: v1.calculla.com. We left the version 1 of Calculla untouched for archival purposes.

Direct link to the old version: "Calculla v1" version of this calculator

Direct link to the old version: "Calculla v1" version of this calculator