With the need to calculate the percent of the people faces constantly, sometimes even without realizing it. And not only on the math exam, but, for example, trying to determine what part of total family income are utility bills or payment for a kindergarten. And many need to count the percent baffled.

### Manual

**1.** Understand that the number from which to calculate interest — it is always hundred percent. Regardless of if there it in the problem or you found it, adding the income of all family members. It can be described, for example, the letter a or any other letter, but can never denote.

**2.** Find that number 1 percent. To do this, the original number, divide by 100. If you take the General formula, the 1 cent and will be equal to a/100.

**3.** Suppose you want to find not 1 percent, and 20. Then the number which designated 1 percent of specified, must be multiplied by the required percentage. That is, get a/100*20. For example, your salary is 11 000 rubles. 1% of this number is 110 rubles, and 20% -2 200 rubles.

**4.** Suppose the problem is to find out what percentage of the initial number a is number b. The amount of interest that you want to find, label as x. Find 1%, which will be a/100. In order to determine how many percent of the number a is number b, it is necessary to divide the obtained value. Remember the rules of integer division on the fraction. The number must be divided into a numerator (in this case) and multiply by its denominator (in this case 100): x=b/a*100. For example, the warehouse brought 250 bags of potatoes. 35 the storekeeper immediately sent to the store, and he needs to know how much it is per cent of the total number of bags. Find 1% which in this problem will amount to 250/100=2.5 bag. Dividing 35 by 2.5, you will receive the sought-for value is 14%.