A percentage is a ratio expressed in terms of a unit being 100. A percentage is usually denoted by the symbol ``%.'' For example, $20\%$ of $\$ 700.47$ is $ $175.12$ (using \htmladdnormallink{fixed point arithmetic}{http://planetmath.org/encyclopedia/FixedPoint3.html} to two \htmladdnormallink{decimal places}{http://planetmath.org/encyclopedia/TenThousandths.html} for display). On most \htmladdnormallink{calculators}{http://planetmath.org/encyclopedia/Calculator.html}, one sure way to \htmladdnormallink{calculate}{http://planetmath.org/encyclopedia/SearchProblem.html} a percentage is by entering a \htmladdnormallink{decimal point}{http://planetmath.org/encyclopedia/DecimalPoint.html} before the desired percentage and multiplying that by the amount one wishes to calculate the percentage of. Some calculators have a percentage key. When tipping at most restaurants in the \htmladdnormallink{United States}{http://planetmath.org/encyclopedia/UnitedStatesOfAmerica.html}, it is customary to tip 15\% of the check to the waiter for parties of as much as four people. One common shortcut is to \htmladdnormallink{divide}{http://planetmath.org/encyclopedia/ArchimedeanSemigroup.html} by 10 (by moving the decimal point to the left) and then add half of that amount. Note that the percentage symbol \% (Shift-5 in most American keyboard layouts) is \htmladdnormallink{overloaded}{http://planetmath.org/encyclopedia/Overload.html} in \TeX{} as a comment start indicator and in \htmladdnormallink{Mathematica}{http://planetmath.org/encyclopedia/Mathematica.html} as a shortcut for referring to the previous output. \end{document} $