Percentage Calculations You Use Without Realizing
Percentages show up in discounts, tips, interest, and taxes. After a few costly mistakes, I sat down and actually learned the math I use regularly. Percentages show up everywhere in daily life: discounts, tips, interest rates, tax, and statistics. I used to do them in my head and hope I was close enough. After a few costly mistakes, mostly around discounts that were less generous than they looked, I sat down and actually learned the math. Here is what I use regularly, with the shortcuts that have saved me time and money. The Three Calculations That Cover Most Cases Almost every percentage problem is one of three types. First, finding a percentage of a number: what is 15 percent of 80. Multiply 80 by 0.15 to get 12. Second, finding what percentage one number is of another: 30 is what percentage of 120. Divide 30 by 120 to get 0.25, which is 25 percent. Third, finding the percentage change between two numbers: a price went from 40 to 50, what is the increase. Subtract 40 from 50 to get 10, divide 10 by 40 to get 0.25, which is a 25 percent increase. Once I had these three patterns clear, most percentage problems became routine. The trick is recognizing which type a problem is before reaching for the calculator. A store sign says 30 percent off. That is type one.