This little 15-minute TedTalk, Arthur Benjamin races calculators from the audience doing the calculations in his head. He is very entertaining and I think students would enjoy the presentation, since they are often under the impression that nobody has every done calculations without a calculator. He squares a random 4-digit number from the audience in his head just as fast as the calculators.

For those of you that teach probablity, he does a neat trick guessing the missing digits of 7-digit numbers (this is somewhere around the 7-minute mark).

For elementary ed, there is a nice “number” on guessing the day of the week when someone was born based on the birth date (8-9 minute mark).

For you algebra teachers, he does the square of a 5-digit number, going through the thought process out loud (starting around the 11-minute mark). Cleverly, he squares the number by breaking it into a binomial: (57683)^{2} = (57000+683)^{2} = 57000^{2} + 57000*683*2 + 683^{2}

Dr. Maria Andersen has spent most of her career teaching, writing curriculum, and developing digital products for learning. Recently she returned to the classroom, having new teaching adventures in K-12 middle and high school.