I am not liking this book. Previous maths books by the author were amazing because the author is great at explaining the essence and beauty of maths itself. There are occasional morsels of that in this book, which are enjoyable, but unfortunately most of the book is taken over by the idea of "the shortcut" applied to real life situations supposedly inspired by the maths. It just doesn't work. The author tries too hard to find "shortcuts" in real-life somehow related to the maths, but the relation is not there... it ends up being shoehorned in, filler material with lots of words but little content, interviewing people trying unsuccessfully to extract "shortcuts" from them, which on several occasions ends up being a bit cringe and child-like. Real-life examples are unsupported by evidence (no indication of serious research, no references) and most of the time they are just obvious trivial boring statements.
An example of what I mean: a really nice mathematical fact is given - to calculate something in the real domain, you can take a shortcut through the complex domain and back (amazing, no need to find real-life shortcuts!). The author then interviews the creator of lastminute.com, shoe-horning the following "analogy" to the shortcut over complex numbers "Hoberman’s success was that he took advantage of the amazing shortcut that the internet provided in those early days of the dot-com boom. Time and again it allowed one to cut out the middle men. In the case of lastminute.com it was the travel agent.".... ok. It's at best loosely related, and at worst a very boring and trivial comment. I'd rather read only about the mathy bits!!
Another example: talking about the maths of map-making (projecting a sphere into a planar map) suddenly the discussion turns to mind maps "Called mind maps, their purpose is to tease out interesting connections between different ideas that you might be exploring. Mind maps have for years been the staple diet of students trying to cram for exams because they help to create an integrated story of a subject that in words can feel too difficult to navigate."... ok.
Another example: In a chapter about probability and chance, the conversation goes into markets, interviewing a historian, "if you were reading this pitstop in the hope that I have some cunning shortcuts to how to invest your savings, my advice would be to combine the skills of the mathematicians together with exploiting the deep knowledge that someone like Helen has gleaned through her training as a historian to be able to guess the next episode in the soap opera that we call the markets."
Some things I liked, though: the scaling advantage of big cities (doubling size gives extra 15% more of everything, on top of doubling), the counting-to-60-in-2-hands system using fingerbones, the trick to win Nim, the removing-beans game, converting each pile to binary and adding them, the trinary system with negative digits (-1,0,1) (never knew you could do that!!), going over 1/e of a full population is enough to almost guarantee getting the "best" if you keep the next highest.