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#EverydayMaths Apparently it's National Numeracy Day. So here are a couple of examples of how an experienced mathematician might go about mental arithmetic. The first one is to multiply 29 by 35. To multiply two close numbers, it is often helpful to use ... 1/
the difference-of-squares trick. Here we see that 29x35=(32-3)(32+3) and that equals 32 squared minus 3 squared. A maths nerd like me will know that 32 is 2 to the five, so its square is 2 to the ten, which is 1024. So we just have to subtract 9 from that, getting 1015. 2/
The point there was that it can be done without one having to hold a lot in one's head at once -- assuming one knows a few useful facts about things like differences of squares and powers of 2.
For a second example, let's try 28x91. Another good thing to do ... 3/
For a second example, let's try 28x91. Another good thing to do ... 3/
