"on weekday" or "in weekday", which is right?

Question

Here is the sentence:

It's clearly shown that more people have meals in the restaurant on weekdays thatn at weekends.

Answer 1

On weekdays/on a weekday

Answer 2

That sentence is right. On weekdays is gramatically correct, not in weekdays. Or you could say during the week. At the weekend is also correct although most people prefer to say on the weekend.

Answer 3

It's clearly shown that more people eat in restraunts on weekdays than on weekends.