2.2.0 :011 > (50..99).each{|x| puts "#{x}+#{x}=#{2*x}" if x%10 == 2*x/100 && 2*x/10%10 == 2*x%10  }
61+61=122
 => 50..99 

# ab+ab = bcc 
# x%10 == 2*x/100 即：x的个位要等于2x的百位
# 2*x/10%10 == 2*x%10 即：2x的十位和个位数字要相同 cc