We were taught to find a percentage of the number at school, but over time, many adults have this important skill is lost. Nevertheless, when you are trying to calculate the size of the discount in the store or determine the amount of money that needs to be postponed every month to accumulate a dream for a vacation, you will need the right mathematical formula.
"Take and do" will show you several ways to calculate the percentage of the amount that can be used in different situations.
1. How to find a percentage of
Basic rule
If you want to calculate the percentage of any number, you should use the formula P% * x = y, where:
- P% is the percentage;
- X - number;
- Y - final answer.
For example, you need to count how much money you will save, buying a smartphone, which costs $ 250, with a 20% discount.
- In this case, the equation will be as follows: 20% * 250 = y.
- To produce mathematical calculations, you need to convert 20% in a decimal fraction. Just divide the number 100 and remove the percent sign.
- Change the equation: 0.2 * 250 = y.
- Calculates: 0.2 * 250 = 50. Answer: Y = 50.
Buying a smartphone with a 20% discount, you will save $ 50.
Alternative way
There is another way to calculate the percentage that can be useful when you do not have a calculator at hand, but it was not easy to solve the equation in mind. Suppose you again need to find out what amount is 20% of 250.
- To do this, you can multiply the numbers, dropping zeros: 2 * 25 = 50.
- Then you need to understand what to do with zeros that you did not take into account when multiplying numbers. Thus, in response can be 50; 0.5 or 500.
- Of the 2 last numbers, one is too small, the other is too large compared to 250. It is impossible that 0.5 and 500 are 20% of 250. Therefore, the correct answer: 50.
If you are dealing with more complex numbers, you can change this method slightly. Suppose you need to calculate 34% of 45.
- Spread 34% by 30% and 4%.
- The equation is obtained in such: (30% + 4%) * 45.
- Consider: (30% + 4%) * 45 = 13.5 + 1.8 = 15.3.
Answer: 15.3. Another example is calculated 40% of 154.
- Start with decomposition 154 at 150 and 4.
- Thus, the equation will be as follows: 40% * (150 + 4).
- Calculates: 40% * (150 + 4) = 60 + 1,6 = 61.6.
Answer: 61.6.
2. How to calculate what percentage certain number is from more
If you need to calculate, what percentage is a certain number from a larger amount, you need to use the Y / X = P% formula. For example, suppose that of the birthday of $ 80 presented to you on the birthday of $ 80 and now you want to calculate what percentage of the presented amount you have already spent.
- In this case, y = 20, x = 80.
- The equation is obtained as follows: 20/80 = p%.
- Calculate: 20/80 = 0.25.
- Then you need to convert a decimal fraction in interest. To do this, multiply the resulting number per 100.
- Thus, 0.25 * 100 = 25%. Answer: 25%.
So you spent 25% of the $ 80 donated.
3. How to determine the number if you know what is equal to the percentage of it
If you need to calculate an integer, considering that you know what is equal to the percentage of it, you need to use the Y / P% formula = X. For example, you saw an advertisement in which you will save $ 40, that is, 20% of The total cost of a trip for the weekend, if you book it right away. You are interested in learn the total cost of the trip. Since the announcement does not say anything about this, you decide to calculate it yourself.
- In this case, y = 40, p% = 20%, and X is unknown.
- The equation is obtained as follows: 40/20% = X.
- Turn 20% in decimal fraction: 20/100 = 0.2.
- The equation will be like this: 40 / 0.2 = X.
- Consider: 40/0,2 = 200. Reply: 200.
The total cost of the trip is $ 200.