As both a football fan and mathematics educator, I was not only thrilled by the Texans’ win against the Tennessee Titans this past Sunday, but also just as thrilled to watch a post-game news conference during which Houston quarterback, Ryan Fitzpatrick, asked his 8-year old son to perform mental math. Fitzpatrick asked a reporter to give his son, Brady, two numbers between 90 and 99 inclusive. After Brady successfully multiplied the numbers 93 and 97 in his head in a matter of seconds, the proud father yelled, “Boom!” Watch the video here.
A couple of posts have already discussed the trick including this one from the Houston Chronicle. There are a couple versions of the trick, but one version goes like this:
Let’s use the two numbers that Brady was given to multiply as an example: 93 and 97.
1. First, subtract each number from 100:
100 – 93 = 7
100 – 97 = 3
2. To get the first two digits of the product of 93 and 97, find the sum of the two differences from step 1 — in this case, 10 — and subtract the sum from 100: 100 – 10 = 90
3. To get the last two digits of the product of 93 and 97, multiply the differences from step 1: 7 × 3 = 21
4. We now have all four digits of the product: 9021
The question remains…why does this trick work?
We challenge you and your students to think about this question and ask you to either post a response or email me at afisher@rice.edu. If you need a hint, let me know at the same email address.
And thank you, Ryan Fitzpatrick, for highlighting the academic achievement of your son! Well-played!