This activity can be used as an ice breaker, especially if students don't know the teacher (or each other, if you choose the variation below).

Objective: To have students make guesses about the teacher and get to know him/her better.
Proficiency Level; High beginners and above
Age Level: Any
Materials: None

Choose some significant numbers in your life (your birthday, your age, the number of children/pets you have, how long you have lived where you live now, how many times a week you exercise, how long you've been a teacher, etc.). Write them on the board, randomly, and ask students to guess what they refer to. Their curiosity will almost certainly drive them to make several guesses, and if nobody can guess correctly about any number, tell them the answer at the end.

Variation: If students don't know each other, they can do the same on a piece of paper and go around the classroom, making guesses about their peers and answering questions about them.