Percentage means per cent or per hundred. It is a way to express a number as a fraction of 100. For example, 50% of a number means   or half of the number. Similarly, 25% of a number is one fourth of the number; 20% means one fifth of the number etc. Hence percentage indicates the part or fraction of a number. Percentage can be calculated as: \[x\;\% \;{\rm{of}}\;y = \frac{{xy}}{{100}}\]

For example 35% of 200 is equal to \(\frac{{35}}{{100}} \times 200 = 70\) 

Example 01: 40% of the voters promise to vote for A and the rest promise to vote for B. Of these, on the last day, 15% of the voters went back on their promise to vote for A and 25% of voters went back of their promise to vote for B and A lost by 20 votes. Then the total number of voters is: 

Solution: Initially 40% and 60% promised for A, B respectively, on the last day 15% of 40  and  25% of 60 went back from promise to vote A, B respectively.
So A got 40% + 25% of 60 – 15% of 40 = 49% votes
B got 100 – 49 = 51% votes 

Therefore B won by 51 – 49 = 2 % of total votes

Given that 2% of the total votes = 20, hence the total votes = 1000.