Accurate decimal math in Ruby with BigDecimal

gistfile1.txt

2.1.0 :009 >   0.3.class
 => Float 
 
2.1.0 :010 > 0.3 - 0.1
 => 0.19999999999999998 

2.1.0 :011 > require 'bigdecimal'
 => true 

2.1.0 :012 > BigDecimal.new(0.3, 10) - BigDecimal.new(0.1, 10)
 => #<BigDecimal:1011802e8,'0.2E0',9(18)> 

2.1.0 :013 > (BigDecimal.new(0.3, 10) - BigDecimal.new(0.1, 10)).to_s
 => "0.2E0" 

2.1.0 :014 > (BigDecimal.new(0.3, 10) - BigDecimal.new(0.1, 10)).to_f
 => 0.2