Rounding in Ruby String Format

Ruby has a nice sting format operator, % for formating in a sprintf-like fashion:

$ irb

irb(main):001:0> "%2.1f" % 12.8987987

=> "12.9"

Works well, but the rounding can be correct:

irb(main):002:0> "%2.1f" % 2.85

=> "2.9"

or incorrect:

irb(main):003:0> "%2.1f" % 12.85

=> "12.8"

To compensate, use round and some decimal-place finangling:

irb(main):004:0> "%2.1f" % ((12.85*10.0).round/10.0)

=> "12.9"