Kevin listened for the first ten minutes and then his eyes wondered. “The red head…she has the greatest pair of…”
The lecture was called “The Joy of 9”*. So far Kevin felt no joy.
….Let’s consider why that works. Call the first number you consider as ‘x’….tripling that x gives you 3x…when you add 6, that makes 3x+6…Triple that will make 3(3x+6), or 9x+18…….
“Oh, Debbie. Sweet Debbie, how I love your…”
….do an example like this: 3, 456. Adding the digits together and we have 18, and 18 is a multiple of 9. And, guess what? 3,456 is a multiple of 9! What about 1,234? Its digits add up to….
Kevin’s gaze swung over to the girl sitting in the row below him, Karen. She was doodling. Not only doodling, Karen was doodling semi-porn doodles. “Dang! She’s good!”
While he watched, the Joy of 9 continued. …How about a bigger problem: 91,787+42,864. If we add those wonderful numbers together correctly, we will arrive at 134,651. If we check our answers, we add the digits to get 20; then add 2+0 and get 2…
The Joy of 9 lecture concluded with “…and the resulting number is 9…therefore…”
Kevin and the class staggered out the lecture hall. Kevin caught up with…
Who do you think Kevin will choose? Will he borrow someone’s notes? Will he pass the next exam?
*This lecture was partially derived from The Joy of Mathematics by Professor Arthur T. Benjamin. Words have been changed from the lecture to avoid copyright infringement. No insult was meant or implied to Dr. Benjamin. My husband would hang on his every word, while I would be the one dozing off.
P.S. My husband reads stuff like this, even has a video of Professor Benjamin presenting the real lecture. He watches videos like this. And, he tries to share the ideas with me.
The next time a program on “Joy of Quilting” I am on that like fly on molasses.