To quickly estimate the discount you will receive when using a 30 percent off coupon, start by dividing the total cost of your items by 10, and then multiply this number by three, according to FinancesOnline. For example, if your total cost is $12.30, then 10 percent of this is $1.23, which corresponds to moving the decimal point one place to the left. Therefore, 30 percent is $1.23 multiplied by 3, or $3.69.
It is often easiest to begin by determining what 10 percent of the total cost is and then working with that number to determine the total discount, states FinancesOnline. Multiplying by 10 percent is equivalent to multiplying by 0.1 or dividing by 10. It can also be helpful to form an estimate by rounding decimal points to the nearest 10 or 100. For example if your total price is $18.99, you can round up one cent to $19.00. In this case, 10 percent of the total comes to $1.9, and multiplying this by three makes $5.70, which is 30 percent of $19.00. This estimate is very close to 30 percent of the original price.
To determine a discount of 5 percent, start by dividing the total by 10, and then divide this value by two, according to FinancesOnline.