Theory:

1. Finding a percentage of a given number:
  
To find the percentage of a given number, multiply the number by the require percent.
 
Let the number \(= x\)
 
Require percent \(= p\)\(\%\)
 
Percentage of given number \(= p\)\(\%\) of \(x\)
 
\(=\) p100×x
 
 
2. Finding the original number from its percent:
  
Let original number \(= x\)
 
Require percent \(= p\)\(\%\)
 
Obtained percentage \(= y\)
 
Now \(p\)\(\%\) of \(x = y\)
 
p100×x \(= y\)
 
\(x =\) yp×100
 
Number \(=\) \(\frac{\text{Obtained percentage}}{\text{percent}}\)\(\times100\)
 
 
3. Finding how much percent one quantity is of another quantity:
 
To find what percent of one quantity is of the other quantity if two quantities are given, we proceed as:
 
Let \(a\) and \(b\) are two quantities and we want to know 'what percent of \(a\) is \(b?\)'.
 
Let \(x\)\(\%\) of \(a\) is equal to \(b\) then:
 
x100×a=bx=ba×100