Thanks for providing these questions.

I decided to have a look at Question 2 and have a few comments, though I understand you are only providing what has been provided to you.

I was surprised ...

1. ... to see that the definition of most "efficient" formula was "the formula with the least number of characters" as opposed to, say, "the formula that calculated the fastest".

2. ... that the stated solution was given as such, with no "robustness" required. I have two reasons:

(i) I did not see in the given written information that the "original square" must start in cell D4 or below/right, it just refers to "a range of numbers next to the blue cells". Yet if the original square does start above/left of D4, the stated solution is not a solution at all.

(ii) The stated solution also relies on certain other things happening (or not happening) in the cells above and left of the "original cells" For example, if cell B15, which has nothing to do with the stated challenge, has the value 100 entered into it, the stated solution returns, without warning, an incorrect result in cell J18.

3. ... that the particular OFFSET solution was given as an alternative. Again it relies on certain unrelated events not happening. For example, if any rows/columns above/left of the "original square" are either deleted or inserted, the solution produces incorrect results.

For what it is worth, I would have used this much longer formula (but more robust and easily scalable to a larger grid - unlike the INDEX alternative suggested) in J18, copied across and down.

=INDEX($E$18:$H$21,ROWS($E$18:$H$21)-ROWS(J$18:J18)+1,COLUMNS($E$18:$H$21)-COLUMNS($J18:J18)+1)