He then went to see the oranges being harvested. He found out that they harvest 49 sacks per day and discard 2 of them. How many oranges do they harvest per day if each sack contains 10 oranges?
1. He sees 49 sacks being harvested per day. 
2. He sees that 2 of those sacks are discarded. 
3. He knows that each sack contains 10 oranges. 

So we can say that: 

49 sacks - 2 sacks = 47 sacks 

47 sacks x 10 oranges = 470 oranges 

Therefore, they harvest 470 oranges per day.