Seeing this video from Howie Hua’s video shorts collection reminded me of a site, I like, Mudd Math Fun Facts, which is where I first came across the squares ending in 5 trick.
This searchable collection, Mudd Math Fun Facts from Harvey Mudd College Math Department, has resources that can make great starter activities. Perhaps try Squares Ending in 5 and Multiplication by 11 both made excellent starters. I have looked at proofs for these with students as well as enjoying the mental Maths tricks!
It is possible to search by topic, difficulty level and keywords.Examples to try:
- Multiplication by 11
- Difference of Squares
- Magic 1089
- Squares Ending in 5
- Multiplying Complementary Pairs
- Kaprekar’s Constant
These all come from the lightning arithmetic category, where we also find Squaring Quickly. In each article, you will find presentation suggestions – ideas for presenting to students, the math behind the fact, and references.