2021 AMC 10B Problems/Problem 8
Problem
Mr. Zhou places all the integers from 
to 
into a 
by grid. He places in the middle square (eighth row and eighth column) and places other numbers one by one clockwise, as shown in part in the diagram below. What is the sum of the greatest number and the least number that appear in the second row from the top?
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Solution 1
By observing that the right-top corner of a square will always be a square, we know that the top right corner of the x grid is . We can subtract 
to get the value of the top-left corner; 
. We can then find the value of the bottom left and right corners similarly. From there, we can find the value of the box on the far right in the 2nd row from the top by subtracting 
, since the length of the side will be one box shorter. Similarly, we find the value for the box 2nd from the left and 2nd from the top, which is 
. We know that the least number in the 2nd row will be , and the greatest will be the number to its left, which is less than . We then sum and 
to get 
.
-Dynosol
Video Solution by OmegaLearn (Using Pattern Finding)
~ pi_is_3.14
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