To calculate a percentage, multiply the two numbers together and divide the result by 100, using the following formula: A x B / 100. For example, if we want to know how much is 30% of 150, just multiply 30 x 150 and then divide the result by 100. Then, we will have 4500 (return of 30 x 150) / 100 = 45. The concept is simple: take 30 units of a number divided into 100 parts; practically, we consider 1 hundredth of 150 which is equivalent to 1.5 and we calculate the desired percentage (in this case, 30) making a multiplication. Thus we will have 1.5 x 30 = 45. The same result is get using the proportion "A: C = B: 100", where A represents the unknown number that we want to know, C is the total and B is the number that quantifies the percentage (100). The relationship between the two numbers will be A: 150 = 30: 100. Since in the proportions the product of the means (30 and 150) is equal to the product of the extremes (A and 100), to know the unknown number A we will have to multiply 30 x 150 and divide the result by 100, obtaining 4500 : 100 = 45. Another explanation of the concept consists in transforming the percentage into a fraction (30% = 30/100, where 30 is the numerator and 100 is the denominator) to multiply by the number which represents the total (0.3 x 150).
In this page, the first calculator (the most used) has been joined by another 9, each of which shows the formula used and the explanation of the result, using the Direct Calculation and the Calculation of Inverse Percentage.
Attention: for decimals use the dot and not the comma (,).