This will take a starting number, ending number, and group size and it will return an array of groups [rangeStart, rangeEnd]

equal_div.rb

# Example use:
#
# 1.9.3p392 :000 > equal_div(432,239842934,22)
#   => [[432, 10902364], [10902365, 21804297], [21804298, 32706230], [32706231, 43608163], [43608164, 54510096], [54510097, 65412029], [65412030, 76313962], [76313963, 87215895], [87215896, 98117828], [98117829, 109019761], [109019762, 119921694], [119921695, 130823627], [130823628, 141725560], [141725561, 152627493], [152627494, 163529426], [163529427, 174431359], [174431360, 185333292], [185333293, 196235225], [196235226, 207137158], [207137159, 218039091], [218039092, 228941024], [228941025, 239842934]]
#
# 1.9.3p392 :001 > equal_div(432,239842934,4)
#   => [[432, 59961058], [59961059, 119921685], [119921686, 179882312], [179882313, 239842934]]
#

def equal_div(first, last, num_of_groups)
  total      = last - first
  group_size = total / num_of_groups + 1

  top    = first
  bottom = top + group_size
  blocks = 1.upto(num_of_groups).inject([]) do |result, x|
    bottom = last if bottom > last
    result << [ top, bottom ]

    top    += group_size + 1
    bottom =  top + group_size

    result
  end

  blocks
end