While using the article repeatedly, we need to take special care. For example
This movie is black and white.
This means the movie has only two colours- partly white and partly black.
He has a brown and a white dog.
This means that he has two dogs- one brown and another white.
Hence when we use two articles, the objects also become separate.
A friend and mentor is hard to get.
Here friend and mentor are associated with the same person. So in the second case, we didn’t use article.
The principal and the vice-principle honoured the meritorious students.
Here the Principal and the Vice-Principal are two different persons. So we have used the article in both the cases.
Another case is when the two nouns refer to the same person and there is a comparison.
He is a better batsman than bowler.
Here batsman and bowler refer to the same person. So in the second case there was no article