Rails 3.2.8 - How do I get the week number from Rails?

Question

I would like to know how to get the current week number from Rails and how do I manipulate it:

1. Translate the week number into date.
2. Make an interval

Answer 1

date.commercial([cwyear=-4712[, cweek=1[, cwday=1[, start=Date::ITALY]]]]) → date
Creates a date object denoting the given week date.

The week and the day of week should be a negative 
or a positive number (as a relative week/day from the end of year/week when negative). 
They should not be zero.

For the interval

require 'date'

  def week_dates( week_num )
    year = Time.now.year
    week_start = Date.commercial( year, week_num, 1 )
    week_end = Date.commercial( year, week_num, 7 )
    week_start.strftime( "%m/%d/%y" ) + ' - ' + week_end.strftime("%m/%d/%y" )
  end

  puts week_dates(22)

EG: Input (Week Number): 22

Output: 06/12/08 - 06/19/08

credit: Siep Korteling http://www.ruby-forum.com/topic/125140