Solution

(related to Problem: Digital Multiplication)

The solution that gives the smallest possible sum of digits in the common product is $23 \times 174 = 58 \times 69 = 4,002,$ and the solution that gives the largest possible sum of digits, $9 \times 654 = 18 \times 327 = 5,886.$ In the first case, the digits sum to $6$ and in the second case to $27.$ There is no way of obtaining the solution but by actual trial.


Thank you to the contributors under CC BY-SA 4.0!

Github:
bookofproofs
non-Github:
@H-Dudeney


References

Project Gutenberg

  1. Dudeney, H. E.: "Amusements in Mathematics", The Authors' Club, 1917

This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this edition or online at http://www.gutenberg.org. If you are not located in the United States, you'll have to check the laws of the country where you are located before using this ebook.