.
Decomposition of the integer number of 40 into the profuct of prime integers is
40 =
.
From this decomposition, it is clear that the number which multiplied by 40 gives a perfect square is 2*5 = 10.
Indeed, 10*40 = 400 =
.
Also, it is clear from the decomposition, that 2*5 = 10 is the MINIMAL integer number with such a property.
Solved, answered, explained and completed.