Jesus' original disciples were selected by Him and called apostles. How many were there?
Jesus, when He was on earth, had many, many followers. The Bible says in the Gospel of Luke, "And it was at this time that He went off to the mountain to pray, and He spent the whole night in prayer to God. And when day came, He called His disciples to Him; and chose twelve of them, whom He also named as apostles..."
So the original group of apostles were 12 apostles who Jesus chose. If someone said "there were 12 original apostles" they would be correct.
At the same time, one of the 12 apostles, Judas, betrayed Jesus and left the other disciples. So he was no longer one of the disciples. The other disciples selected one of the other followers of Jesus, named Matthias; and it says in Acts "he was numbered with the eleven apostles."
So there were 12; then there were 11 faithful ones; and now there is another one to make up the 12. So there were 13 total people who were named original apostles.
The apostle Paul was not one of the original followers of Jesus, but He was a dedicated follower of Jesus who believed in Jesus after Christ was raised from the dead. So could you call him a 13th -- or a 14th -- apostle?
So the first answer is the easiest -- there were 12 original apostles.