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by mkl
749 days ago
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You need to escape those *s with \ or put spaces around them. This kind of method works much more generally. E.g. 58×33 will be close to 60×30 = 1800, so 58×30 = 1800 - 2×30 = 1740, so 58×33 = 1740+3×58 = 1740+3×60-3×2 = 1740+180-6 = 1940-20-6 = 1914. Similarly 27×7 = 30×7-3×7 = 210-21 = 189, 270×7 = 10×27×7 = 10×189 = 1890, etc. |
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