Calculating percentages in not a difficult task, as it involves just two steps. First, you have to multiply the part by 100 and then divide this product by the whole. For example, if you want to find out the percentage of the 14 female guests to a party, out of a total of 40 guests, then you must do (14 × 100) / 45 = 1,400 / 40 = 35 percent.
Transforming percentages into quantities is much more straightforward than dealing with fractions. Suppose you have taken a loan of $2,700 and the lender informs you that the interest rate is 2/5 of the total amount. In this case, you have to multiply by 2 and find $5,400, before dividing by 5 to come up with the $1,080 interest. However, if the lender told you the interest rate is 40 percent, you only need to multiply $2,700 by 0.40 to find $1,080.
Percentages help you understand how big a part is compared to a whole. Calculating percentages is especially useful when the parts and the whole are not simple numbers, such as two pieces in a four-piece pizza, but values that are difficult to visualize. For example, you can either say that the number of people who voted for a specific mayoral candidate was 13,750 out of 26,450, or that the candidate got 52 percent of the votes, which is easier to interpret.
You can compare percentages immediately, without needing to alter them in any way. For example, if you are told that 40 percent of people in an area like the color green and 30 percent prefer red, you can instantly say that "reds" are less, as 30 < 40. However, if you are given that greens are 2/5 of the total population and reds are 3/10, you first have to find the fractions' common denominator before making a comparison, which is a more tedious task.