gmat prep

1)
The smallest could be -10 and the biggest -1 --> -10*-1=10
But the list wan have -10 -6 and -1 or -10 -6 -2 -1
For one list the product of the integers will be negative and for the other positive.
Insufficient.

2)
The fact there is an even number of members in the list does not tell us how many are even and how many are odd numbers.
For example, one list can be -6 -2 1 2 and the other -6 -2 -1 2
One is positive, the other negative.
Insufficient.

1)and2)
With 1) you know that either the serie only has positive numbers or the serie has only positive numbers.
The product of a serie will only positive numbers is positive.
The product of a serie with only negative number is positive if the number of negative number is even (thanks to 2)
So it is sufficient --> C

Thanks for that