The term per cent mean 'for every hundred'. "A per cent is a fraction whose denominator is 100 and the numerator of the fraction is called the rate per cent." Per cent is denoted by the sign '%'.
Concept to Caluculate Per cent
If we have to find y% of x, then y% of x=(x*y)/100
Expression per cent (x%) into fraction. Required fraction=x/100
Conversion of fraction into Percentage
Expressing a fraction (x/y) in per cent. Required percentage=(x/y)*100)%
Expressing One Quanity as a Per Cent with Respect to Other
To express a quantity as a per cent with respect to other quantity following formula is used.(The quantity to be expressed in per cent)/ (2nd quantity (in respect of which the per cent has to be obtained))X100%
Important Concept and Tricks
 If x% of A is equal to y% of B, then z% of A=(yz/x)% of B
 When a number x is increased or decreased by y%, then the new number will be (100+y)*x/100
 When the value of an object is first changed (increased ) by a% and then changed (increased ) by b%,then Net effect=[a+b +ab/100]%
 Suppose in an examination, x% of total number of students failed in subject A and y% of total number of students failed in subject B and z% failed in both the suject. Then,
 (i) Percentage of students who passed in both the subjects=[100(x+yz)]%
 (ii) Percentage of students who failed in either subject=(x+yz)%
 If due to r% decrease in the price of an item, a person can buy A kg more in Rs.x, then Actual price of that item= Rs (rx)/((100r)A) Per kg
Example :If due to 10% decrease in the price of sugar ,Ram can buy 5 kg more sugar in Rs 100 , then find the actual Price of sugar ?
solution : Here r = 10 % ,x = 100 and A = 5 kg
Actual price of sugar = 10*100/((10010 )*5) = Rs. 2(2/9)
 If the population of a town is P and it increases at the rate of R% per annum, then
 Population after n yr= P(1+r/100)^n
 Population, n yr ago=P/(1+r/100)^n

If the present population of a city is P and there is a increment of R1%, R2% ,R3% in first, second and third year respectively, then
Population of city after 3 yr=P(1+R1/100)(1+R2/100)(1+R3/100)
Example : Population of a city in 20004 was 1000000. If in 2005 there is an increment of 15 % , in 2006 there is a decrement of 35 % and in 2007 there is an increment of 45 %, then find the population of city at the end of the year 2007.
solution : Required population = P (1 + R1/100)(1  R2/100)(1 + R3/100)
= P (1 + 15/100)(1  35/100)(1 + 45/100)
= 1083875