“Hey Google, what’s the factorial of 100?”
There are several clips doing the rounds of what happens when you ask Google Assistant this question. The response is both hilarious and terrifying.
The factorial of 100 is the multiplication of 100 by every whole number less than it. In other words, 100 x 99 x 98 x 97 x 96 x …. x 3 x 2 x 1.
The answer is a big number. Clearly.
Yet Google Assistant gives the wrong answer. Or rather, its answer is rounded up. (Siri abbreviates in a more sensible way.)
Today’s puzzle is to do the sum properly:
How many zeros does the factorial of 100 really have at the end of it?
All that is required to solve this puzzle is knowledge of elementary arithmetic. Such as the fact that, if a number has a 0 at the end, it means this number is divisible by 10.
I’ll be back at 5pm UK with the solution.
PLEASE NO SPOILERS Please discuss your favourite Siri and Google Assistant responses.
UPDATE: The solution is now up here.
I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.
I’m the author of several books of puzzles, most recently the Language Lover’s Puzzle Book. If you are addicted to Wordle, I promise you will like this book. I also give school talks about maths and puzzles (online and in person). If your school is interested please get in touch.
