The two lumberjacks

Once upon a time, there lived two lumberjacks. Their names were Jack and Steve. They were fighting that they were better than each other. Then an old man was moving from there and saw everything. He thought to have a competition between them. He ran and said that you both are selected for a tree cutting competition. The next day, they were at their places but the old man was late. He came and asked them to start. After 30 min Jack stopped for 10 minutes. Then Steve heard that and started to cut his trees faster with overconfidence. Every time they were doing it like this. The time was up. Then the old man went to count. He first went to Jack and started counting. Steve heard that 30 trees were cut by Jack. The old man then went to Steve. Jack heard that 10 trees were cut by Steve. Steve asked how did you do that. That's is impossible. I heard that you stopped for 10 minutes. Then Jack said yes you said true. But in the 10 minutes, I was sharping my axe and that helped me to cut trees.