if mary's age is x years.what will be the present age of mary's niece if her niece is 3 years less than one third of mary's age 5 years ago?

Answer 1

mary's age 5 years ago is x-5
1/3 of that is (x-5)/3
3 less than that is (x-5)/3 - 3

Now, that may not be the answer, since it's difficult to parse just who's how old when, with your unusual verb tenses.