In Dingistan the coins are of the following denomination:
SILVER: 10, 15, and 20 dingos
COPPER: 1, 2, and 3 dingos.
The ACMs (automatic change machines) accept silver coins and return change as follows:
20d=(15+2+2+1) d
15d=(10+2+2+1) d
10d=(3+3+2+2) d

After Dingus converted into copper the 145d he had in silver coins, his friend W.G.Ringus counted them and successfully reconstructed the original composition of silver coins, previously unknown to him.

It is up to you to find both the input and the output
- if the Wise Guy did it – you can do it, too.

It is D4, if solved analytically.

(In reply to Analytical solution (spoiler) (D2) by Steve Herman)

Excellent reasoning!

"So the total number of silver coins can be determined by halving the number of 3c coins.

This observation, unspotted by me, made it a d2 problem.

Seeing this shortcut, saving comparison of distinct partitions credits you with one special word of appreciation:

C  H  A  P  E  A  U  !

Posted by Ady TZIDON on 2014-10-28 11:49:46