This simple problem is from a series of review problems:

problem.jpg

Here is the book's solution:

solution.PNG

Here is what I did:

my solution.jpg

Question 1) Where did the author get the 4? The two largest numbers are 5 and 7 and the difference can only be 2 or -2.

Question 2) Is there a way to solve this problem using algebra? Or is that even expected here?

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