`inject(:+)` vs `each +=`

gistfile1.txt

irb(main):003:0> require 'benchmark'
=> true
irb(main):004:0> numbers = nil
=> nil
irb(main):005:0> puts Benchmark.measure { numbers = 1_000_000.times.map {|i| i.to_f }; 1 }
  1.110000   0.000000   1.110000 (  0.448476)
=> nil
irb(main):006:0> numbers.length
=> 1000000
irb(main):007:0> puts Benchmark.measure { numbers.inject(:+) }
  0.070000   0.000000   0.070000 (  0.060648)
=> nil
irb(main):008:0> puts Benchmark.measure { s = 0; numbers.each {|n| s += n } }
  0.820000   0.010000   0.830000 (  0.587285)
=> nil