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Usually, even young students of the 4-th grade level can solve such problems using a backward method
and making inverse operations in the inverse order.
Solving this way, you make two steps:
(1) You divide 40 and 65 by 5, and you conclude that your numbers are integer numbers between 8 and 13.
(2) Then the next and the last step is to subtract 1 from the numbers, obtained in step (1).
Doing it, you conclude that your original numbers are integer numbers between 8-1 = 7 and 13-1 = 12.
ANSWER. Thus you found out that the original numbers are integer numbers between 7 and 12.
Solved for the 4-th grade level without using equations, with full explanations.