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Russian multiplication




Multiplication by repeated doubling, also known as peasant multiplication. For example to multiply 17 by 13, double the 17 and halve the 13, and add the doubles that correspond to an odd number in the other column.

So
doubled and halved
doubled and halved
doubled and halved
adding up the numbers in the first column that correspond to an odd number in the second
17 × 13
34 × 6
68 × 3
136 × 1
(17 + 68 + 136) = 221


Related category

   • ARITHMETIC