Quote:
If m is an integer, is m odd?
(1) m/2 is not an even integer.
(2) m – 3 is an even integer.
This thread sure had some interesting discussion related to St. 1
Here's
an alternate, visual, way of processing St. 1:
We'll try to get a visual sense of what St. 1 is conveying.
We know that 'Integers' is a subset within the set of ALL Real Numbers. And, this set of 'Integers' is further divided into two subsets - Even and Odd.
So, if I represent the subset 'Even Integers' with Red color, then the blue zone represents 'Integers that are not Even, that is, Odd Integers'. And the white zone represents 'Non-Integers.'

Now, if you are told that a real number X is not an Even Integer, that only means that X doesn't lie in the Red Zone.
Can X lie in the blue zone? Sure it can.
Can X lie in the white zone? It can.
So, if you are told that some real number is not an even integer, you are only sure about what this integer is NOT. This number can be an odd integer, or it can be a non-integer (in other words, a fraction).
So, when St. 1 tells you that m/2 is not an even integer, two possibilities arise:
Case 1. m/2 is an odd integer
=> m = 2*odd = Even integer
Case 2. m/2 is a non-integer.
That is, m is not completely divisible by 2.
That is, m leaves a non-zero remainder when divided by 2.
Now, the only possible non-zero remainder that results when a number is divided by 2, is 1 (because 0 ≤ Remainder < Divisor)
This means, m = 2q + 1
That is, m = Odd integer.
Thus, from St. 1, we see that m can either be an even integer or an odd integer. So, St. 1 is not sufficient to arrive at a unique answer.
Hope this visual representation helped further cement your understanding of why St. 1 is insufficient.
Best Regards
Japinder