The array below represents a set of 16 playing cards, with the A's representing Aces:

 A  5  5  A
 5  2  4 10
 3  8  7  4
 A  A  2  6

Divide the array into sections of adjacent cards so that the sum of the cards' values in each section will be 21. Each Ace can represent either 1 or 11 and you must determine how many sections are needed.

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From Page-a-Day Calendar 2016: Amazing Mind Benders, by Puzzability (Mike Shenk, Amy Goldstein and Robert Leighton), Workman Publishing, NY; puzzle for August 6,7.

(In reply to re: Full solution - SPOILER by Charlie)

ok, Charlie.

Once perceiving that each of  the aces must be counted as 11, the solution was imminent and I did not bother to find out whether there are several solutions or just the one I've found.
Clearly, I did not look for others.

Edited on August 11, 2016, 10:47 am

Posted by Ady TZIDON on 2016-08-11 10:45:09