one.rb

irb(main):016:0> 1 - 0.9
=> 0.09999999999999998
irb(main):017:0> 1 - 0.8
=> 0.19999999999999996
irb(main):018:0> 1 - 0.7
=> 0.30000000000000004
irb(main):019:0> 1 - 0.6
=> 0.4
irb(main):020:0> 1 - 0.5
=> 0.5
irb(main):021:0> 1 - 0.4
=> 0.6
irb(main):022:0> 1 - 0.3
=> 0.7
irb(main):023:0> 1 - 0.2
=> 0.8
irb(main):024:0> 1 - 0.1
=> 0.9
irb(main):025:0> 1 - 0.0
=> 1.0
irb(main):026:0> 1 - 1.0
=> 0.0