What could happen otherwise:

  >>> a = 0.4 * 6 * 5; a
  12.000000000000002
  >>> b = 1.6 * 3; b
  4.8000000000000007
  >>> c = 0.05; c
  0.050000000000000003
  >>> (a * c + b * c) / (a + b)
  0.049999999999999989

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@41891 20353a03-c40f-0410-a6d1-a30d3c3de9de