Ceiling and Floor functions

Just to give some idea of what these guys do:

xs=Table[i,{i,-3,10}];
GraphicsGrid[
{
{Show[
Plot[Floor[x],{x,-3,10}],
ListPlot[Transpose[{xs,xs}]]
],
Show[Plot[Ceiling[x],{x,-3,10}],
ListPlot[Transpose[{xs,xs}]]
]
}
}]
Ceiling[1.5]
Floor[1.5]
Ceiling[1]
Floor[1]

Do you see why it’s called a step function?:)

PostalRates[x_]:=.49+.21Ceiling[x-1]
Plot[PostalRates[x],{x,0,10},AxesOrigin->{0,0},AxesLabel->{"Weight (oz)","Cost ($)"},PlotLabel->"Postal Rates"]