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

 A  3  5  8
10  2  4  9
 4  2  7  A
 2  5  3  8

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 March 9.

The total is  74, 10 below 84=4*21;
so there are 4 partitions and one of the aces is 11, and the other is 1.
The  4 parts are:

11,3,5 from the 1^st row +2 fr the 2^nd row
8 from the 1^st row +4,9 fr the 2^nd row
10 from 2^nd row +4 fr the 3^rd row +2,5 fr the 4^th row
  2,7,1 fr the 3^rd row +3,8 fr the 4^th row.

   

Edited on March 11, 2016, 9:25 am

Posted by Ady TZIDON on 2016-03-11 09:19:53