If five slices of pizza cost $5.50, how much do two slices cost? ten slices? half a slice ?

One slice is $5.50 so 2 slices would be that multiplied by 2.  This will give you $11.  For ten slices, just move the decimal right one place and add a zero.  This will give you $55.  Half a slice you DIVIDE by 2, this gives you $2.75.