Sum all prime numbers until a given number

PrimeFinder

class PrimeFinder
  def initialize
    @prime_list = []
    @prime_sum = 0
  end
  
  def prime?(number)
    sqrt = Math.sqrt(number).to_i
    @prime_list.each do |prime|
      if prime <= sqrt
        if number % prime == 0
          return false
        end
      else
        break
      end
    end
    @prime_list << number
    true
  end
  
  def sum_upto(number)
    # skip even numbers
    (3..number).step(2) do |i|
      @prime_sum += i if prime?(i)
    end
  end
  
  def prime_sum
    @prime_sum + 2
  end
end

require 'benchmark'
Benchmark.bm do |b|
  b.report do
    pf = PrimeFinder.new
    pf.sum_upto(2000000)
    puts pf.prime_sum
  end
end