Decimal.-
-that 
Group: Operators
Aliases: minus
Documentation
Subtract a Decimal or other kind of number from another Decimal, or subtract  a Decimal from another kind of number.
Arguments to - will undergo automatic conversions such that you need not convert other numeric types to Decimal manually.
Arguments
- that: The number to subtract from this.
Examples
Subtracting 10.22 from 20.33.
      a = Decimal.new "20.33"
      b = Decimal.new "10.22"
      c = a - b
      # => Decimal.new 10.11