In the diagram formed of twenty O’s below, in how many ways may four be selected such that they form a square?
What is the least number of O’s that may be removed such that none of these squares remains intact?
O O
O O
O O O O O O
O O O O O O
O O
O O
Note: the horizontal and vertical spacing should be equal.
(I) A total of 21 squares can be constituted as follows:
Dimension # Squares
----------------- ------------------
V13 x V13 2
V8 x V8 4
V5 x V5 2
V2 x V2 4
1x1 9
(II) We need to obviate a minimum of 6 circles such that none of these 21 squares remain intact.
Each of the obviated squares is marked with a hash (#) as follows:
o o
# o
# # o o o o
o o o # # o
o o
o #
Edited on July 25, 2022, 12:11 am
Puzzle Solution
