You will need
  • Calculator.
To find the simple interest rate from a certain amount, multiply the amount of interest on a certain amount and divide by one hundred. As a formula, this rule can be written as follows:PS = C * K% / 100 where:PS – the interest rate
With the amount
To% - the amount of interest.
Employee when applying for a job promised salary: 30000 rubles per month. What amount worker will receive at the end of the month?Solution.
The company is obliged to withhold from the wages of his employee's income tax, the interest rate is 13%. That is, in this case:
30000 * 13 / 100 = 3900 (rubles). Accordingly, the cashier the employee will receive:
30000 – 3900 = 26100 rubles. (In practice this amount might be slightly longer, as usually applied tax deductions, i.e. income tax will be charged on the whole amount).
To determine the inverse of the interest rate, subtract from the sum (with interest) the same amount, divided into one hundred plus the number of interest and multiplied by a hundred. To avoid mistakes when calculating reverse percentages, use a calculator and the following formula:CV = C – C / (100+K%) * 100 where:Ops – back interest rate
– Amount (with interest),
To% - the amount of interest (already accrued).
When calculating the interest rate, be sure to note what data (amount, quantity, weight) given to "clean" or with accrued interest. Example.
On the packaging of mayonnaise says: "+50% free". Mayonnaise is 60 rubles.
Question: what is the amount of mayonnaise added to the package.Solution.
At first glance, the solution is obvious: 50% of 60 rubles – 30 rubles. Usually the "solution" and expect manufacturers. But actually:Ops = 60 – 60/(100+50)*100 = 20 (rubles).As can be seen, the error is 10 rubles, or 50%. Moreover, the manufacturer has specified everything correctly: he put mayonnaise on 40 rubles, and then decided to add (+) mayonnaise in the amount of (20 rubles), representing 50% of this amount (40 RUB.).