A 22-year-old student was tied up and robbed at knifepoint Friday after a man followed her into her building, asked to borrow a pen and then forced his way into her apartment,  according to police reports.

The woman was entering the building, in the 5500 block of N. Kenmore Ave. at about 2:15 p.m. Friday, when a middle-aged black man approached her and began a casual conversation, the report states.

The man told the woman he needed a pen to write a note for a friend in the building. As the victim opened her front door to get a pen, the man forced his way in.

The man took a butcher knife from the kitchen, tied the woman's hands and feet together and stuffed cloth in her mouth. He went through her wallet and desk drawers and fled with $20 in cash and $20 in a change jar.

The woman later managed to untie her feet and went to a neighbor's house to call police.