Ensure each student has a vertical number line from 1 down to 20.

Have each student place a peg on 1 and a peg on 20 on their number line.

Choose a student to think of a mystery number between 1 and 20.

The rest of the students take turns to guess the number and ask the chooser if their number is up (less than) or down (more than) from the mystery number.

The students move their pegs to narrow the range of answers until the mystery number is found.

Repeat by choosing another student to select a mystery number.