Convert percents into decimals by moving the decimal two spaces to the left. For example, 25% = 0.25. Inversely, convert the decimal to a percent by moving the decimal two places to the right. For example, 0.45 = 45%.
Write a percent as a fraction by placing 100 in the denominator and the number next to the percent in the numerator, as 100% = 1/100. Then, reduce to the simplest form. For example, 30% = 30/100 = 3/10.
Calculate the percent of the original value represented by the new value. First subtract the old value from the new value. Divide this difference by the old value, then multiply by 100 and add a percent sign (%). The equation is formed as follows: Percent Change = (End Value-Start Value/Start Value)*100.
Solve simple interest rate problems with percents. Interest is a fee paid on borrowed money. To find the simple interest, multiply the amount borrowed initially (principal) by the duration of the loan and the fixed percentage (rate) on the principal. For example: $10,000 invested for 1 year at an annual rate of 8% will earn $800.
Figure out compound interest problems with percents. Find the first year interest rate by multiplying the initial amount borrowed (principal) by the interest rate. To calculate the interest charged for each successive year multiply the interest rate by the sum of the loan and all previous years' interest amounts. For example, if $100 is invested for 2 years at a rate of 20% compounded semiannually, it will earn $121. The equation is as follows: $100(1+0.20/2)^2*1= $121.