Understand that the number from which to calculate percentages is always one hundred percent. Regardless of whether it is 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, and you do not designate.
Find that number 1 percent. For this original number, divide by 100. If we take the General formula, 1 percent of the number and will be equal to a/100.
Suppose you want to find not 1 percent and 20. Then the number which designated 1 percent of the specified, must be multiplied by the required percentage. That is, will a/100*20. For example, your salary is 11 000 rubles. 1% of this number is 110 rubles, and 20% -2 200 rubles.
For example, the problem is to know how many percent of the original 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 it into the value. Remember the rule of dividing the whole number into a fraction. Need the number to divide into the numerator of the fraction (in this case a) and multiply by its denominator (in this case, 100): x=b/a*100. For example, at the warehouse brought 250 bags of potatoes. 35 storekeeper immediately sent to the store, and he needed to know how much it amounts to 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 get the desired amount to 14%.
Before you take on the task of interest, remember the rules of multiplying and dividing fractions.
When calculating interest, you can use the calculator. But you can experience infinite decimal fraction. It must be rounded.