A neat counting problem I saw on Twitter today

Saw a fun problem in this sequence of tweets today:

Seemed like a great problem to cover with the boys tonight. They had some pretty good ideas right from the start:

Once they had the idea for the first 100 numbers down we moved on to trying to find the 1000th number with no 5’s or 7’s. Their approach was a little different from how I would have proceeded, but it was nice to see their idea. They also noticed and avoided a little trap right at the end 🙂

Really happy I saw this problem today. Excited to get the book when it comes out.

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