Why were the apostles sent out in pairs?

Mark 6:7-12 tells us that Jesus sent his 12 apostles and later 70 disciples (Luke 10:1+2)out preaching from town to town by twos. Preaching of this nature was not easy and two together could encourage and assist one another under dificult circumstances(Luke 10:3 / Matthew 10:16-22) as is stated in principle at Ecclesiastes 4:9+10. As questions were raised among those who were being taught, two disciples together could reach more people, better overcome their objections and find scriptural answers. They were to 'preach and teach' anyone who would listen(Matthew 28:19+20), and having two people with two types of personalities, two minds and two backgrounds, would appeal to different kinds of people they would meet, and reach more hearts. Barnabas, for instance, was at first sent out alone to Antioch, but soon felt the need to have help, and went to find Paul(Acts 11:22-26). Until 'the end', preaching in twos will continue to be a valuable resource (Matthew 24:14) .