Everyday mathematics: numbers you can use
Percent, fractions and estimates in daily life
Many adults think they are bad at mathematics because they had trouble with it at school. But in everyday life most people calculate all the time — when they shop calculate time or split a bill. Everyday mathematics is about using numbers to make good decisions.
§The Four Arithmetic Operations in Practice
Plus, minus, multiply and divide are the foundation. The important thing is to recognize which operation a situation requires. Do you need to add, subtract, multiply or divide into equal parts? Translating a practical situation into the right calculation is often harder than the calculation itself.
§Percent
Percent means 'per hundred'. 50% is the same as half, 25% is a quarter, and 10% is a tenth. When you know these simple relationships, you can often calculate in your head: 10% of an amount is found by moving the decimal point one place, and from there you can build on.
- 0110 % af 250 kr. er 25 kr.
- 025 % is half of 10 %, i.e. DKK 12.50
- 0320 % is double 10 %, i.e. 50 kr.
§Fractions
A fraction describes a part of a whole. In half a pizza, the denominator (the bottom number) is the number of equal pieces, and the numerator (the top) is how many you have. Fractions, percentages and decimals are just different ways of writing the same thing: one half is the same as 50% and 0.5.
§Estimation calculation
Estimation is rough calculation. It is useful when you want to check whether a result is reasonable, or when you need to quickly know if the money will last. Round the numbers to something you can easily calculate with and see if the answer makes sense. An estimate often reveals if you have typed something wrong on a calculator.
The most important thing about everyday mathematics is not to calculate quickly but to understand the numbers well enough to make sensible choices. With practice it becomes a natural part of everyday life.