But multiplying 3783×18926 requires a general multiplication algorithm. An obvious algorithm involves picking the smaller of the two numbers and using it as a counter, repeatedly adding the other number to an ongoing sum. In the case of 3783×18926, this would mean 3783 additions: 0 + 18926 + 18926 + 18926 + ...

Computers are fast, but this is ridiculous, especially if millions of multiplications must be done every second. Therefore, a trick from the 3rd grade is used: multiply one number by just one digit of the second number, and then shift this product over by one place and add that to an ongoing sum:

    18926
  ×  3783
 --------
    56778    (18926 × 3)
  151408     (18926 × 8, shifted left 1 place)
 132482      (18926 × 7, shifted left 2 places)
 56778       (18926 × 3, shifted left 3 places)
---------
 71597058