, here you have given that " Given that the product of five numbers, \(m\), \(p\), \(r\), \(t\), and \(z\), is positive,
Victor314
If m < p < r < t < z and if the product mprtz is positive, which of the following products must be positive?
I. \(mp\)
II. \(rt\)
III. \(tz\)
A. None
B. I only
C. I and II only
D. I and III only
E. I, II, and III
Given that the product of five numbers, \(m\), \(p\), \(r\), \(t\), and \(z\), is positive,
there must be an even number of negative numbers among them (0, 2, or 4 negative numbers). Since it is also given that \(m < p < r < t < z\), we can have the following three cases:
\(m\; |\; p\; |\; r\; |\; t\; |\; z\)
\(+ | + | + | + | +\) (no negative numbers)
\(- | - | + | + | +\) (two negative numbers)
\(- | - | - | - | +\) (four negative numbers)
Let's analyze each option, taking into consideration that the question asks which of them MUST be true, not COULD be true.
I. \(mp>0\)
This option is true for each of the three cases. Therefore, this option is always true.
II. \(rt>0\)
This option is true for each of the three cases. Therefore, this option is always true.
III. \(tz>0\)
If we have the third case, then this option is not true. Eliminate.
Consequently, only options I and II are always true, and thus the answer is C.
Answer: C.