Problem 4
The sum from 1 to 9= 45
The square numbers below 45= 1,4,9,16,25 and 36 (Excluding 0)
Now, We can say that the closest 2 square numbers from 45 are 25 and 36
The difference for each is 20 and 9 respectively.
20 is not an element in our set of numbers from 1 to 10
∴ 9 is the number excluded by Yunji (E)