Start with a number you pick and write on the board. Then come up with a rule in your head and write the result on the board.

Now leave it to students to figure out what operation you performed to come up with your result.

You can adjust this mental math activity based on the level of your students. The rule you use can be very simple, such as basic addition or subtraction or it can be more complicated, such as raising a number to an exponent or a series of operations.

For example, let’s say you begin with the number 7 and you get these results for different levels of students.

7 yields the result 10 (You added 3.)

7 yields the result 2 (You subtracted 5.)

7 yields the result 49 (You multiplied by 7 or raised 7 to the 2nd power.)

7 yields the result 121 (You multiplied by 17 then added 2.)