# Percentage

In mathematics, a percentage (from Latin per centum “by a hundred”) is a number or ratio expressed as a fraction of 100. It is often denoted using the percent sign, “%”, or the abbreviations “pct.”, “pct”; sometimes the abbreviation “pc” is also used. A percentage is a dimensionless number (pure number).

## 1.  Percent implies “for every hundred”. % is read as percentage and x % is read as x per cent.
2.  To calculate p % of y (p/100) x y = (p x y)/100 => p % of y = y % of p
3.  To find what percentage of x is y: y/x × 100
4.  To calculate percentage change in value Percentage change = {change/(initial value)} x 100
5. Percentage point change = Difference of two percentage figures
6. Increase N by S % = N( 1+ S/100 )
7.  Decrease N by S % = N (1 – S/100)
8. If the value of an item goes up/down by x%, the percentage reduction/increment to be now made to bring it back to the original point is 100x/ (100 + x) %.
9. If A is x% more /less than B, then B is 100x/(100 + x) % less/more than A.
10. If the price of an item goes up/down by x %, then the quantity consumed should be reduced by 100x/ (100 + x)% so that the total expenditure remains the same.
11.  Successive Percentage Change If there are successive percentage increases of a % and b%, the effective percentage increase is: {(a + b + (ab/100)}%