Это тест разных видов округллений и их комбинаций при валютном обмене

Округление.rb

def round_math a
  (a*100).round.to_f/100
end

def ceil_math a
  (a*100).ceil.to_f/100
end


def floor_math a
  (1*100).floor.to_f/100
end


def forward a
  round_math a
  # ceil_math a
  # floor_math a
end

def back a
  round_math a
  # ceil_math a
  # floor_math a
end

wrong, total = 0, 0
for i in (100...300)
  for j in (1...31)
    x = i.to_f + ((rand*100).round.to_f)/100
    f =  round_math 1 - j.to_f/100
    delta_x = back(forward(x/f)*f)
    if x != delta_x
      p '--------------------------------'
      p "x = #{x}; f = #{f}"
      p "round(x/f) = #{forward(x/f)}"
      p "round(round(x/f)*f) = #{delta_x}"
      p '--------------------------------'
      wrong += 1
    end
    total += 1
  end
end

p "total = #{total}"
p "wrong = #{wrong}"
p "error = #{wrong.to_f/total}"