A classic in the Math field is How to Solve It by Georg Polya https://www.amazon.com/How-Solve-Mathematical-Princeton-Scie... (https://www.amazon.com/How-Solve-Mathematical-Princeton-Science/dp/069111966X) And for improving statistical thinking, the classic How to Lie With Statistics by Darrell Huff https://www.amazon.com/How-Lie-Statistics-Darrell-Huff-ebook... (https://www.amazon.com/How-Lie-Statistics-Darrell-Huff-ebook/dp/B00351DSX2/)
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