# Wrong, But Useful: Episode 68

/podcasts/wbu68.mp3

In this month’s thrilling installment of Wrong, But Useful, we’re joined by @c_j_smith, who is Calvin Smith in real life.

We discuss…

**Number of the Podcast:**5- Are Fish and Chip shop owners good at maths?
- Two maths puns and a maths joke
- Are there ‘popular’ books that ‘lead you in’ to mechanics?
- An application of the sum-of-squares problem
- Via @PaulsPrattle (Paul O’Malley): “If you were the ruler of the universe tomorrow what would be the objective in secondary mathematics learning for all kids everywhere?”
- Via @aap03102, (Chris Smith)’s newsletter: some love for Simon Plouffe
- Via @christianp: The Big Mathoff is running again
**Puzzle feedback from last time**: We hadn’t seen any solutions when we started recording, but some have come in since - we’ll mention those next month. However: Chris pointed out a tweet from @mathsjem (Jo Morgan) showing the clock-hands puzzle in Thompson’s Practical Algebra, published in 1878.**New Puzzle**: There are 3 lighthouses. The first shines for 3 seconds and then is off for 3 seconds. The second shines for 4 seconds and then is off for 4 seconds. The third shines for 5 seconds and then is off for 5 seconds. Initially, all three come on together. When is the next time they’re all on at the same time?