How Math Explains the World
A Guide to the Power of Numbers, from Car Repair to Modern Physics
James D. Stein
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preface
- Any two-digit number can be written as T+U, where T is the tens digit and U the units digit. Reversing the digits gives the number U+T, and subtracting the second from the first yields T+U-(U+T)=T-9 U=(T-U), which is clearly divisible by 9.Mar 30 2024 1:15AM