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Victor314
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mprtz is positive, therefore, you have 3 scenarios:

1) all 5 are positive
2) 2 lowest are negative, 3 positive.
3) 4 lowest are negative, 1 positive.

I. mp
The 2 lowest, or are both positive (scenario 1), or both are negative (scenario 2 & 3), therefore their product will be positive.

II. rt
The 3rd and 4th term. They are both positive (scenario 1 & 2) or both are negative (scenario 3), therefore their product will be positive.

III. tz
4th and 5th term. They are both positive (scenario 1 & 2), but in scenario 3, t may be negative, and z will always be positive, resulting in a scenario where their product may be negative.

The answer will be C. I and II only must be positive.
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karishmaB Could you pls explain this why cant M be negative and P be positive?
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karishmaB Could you pls explain this why cant M be negative and P be positive?
­P > M

Therefore, it isnt possible P to be negative, and M not.

It cant be M to be negative, and P to be positive, because m*r*p*z*t product is positive, it means you either have zero negatives, 2 negatives, or 4 negatives. So, if M is negative, P must also be negative.
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KarishmaB @Bunnuel

this is a ' must be true ' question right so that means we have to pick scenarios that is 100 percent the truth.

if all 5 are positive which is also a valid scenario, then C won't be the answer right?
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For the product of 5 numbers to be positive, even number of numbers will be negative, if at all there are negative numbers. Note 0s are are out as the product is positive

Also, given m < p < r < t < z, we start from the left

Either both m and p are negative or m, p, r and t all are negative

Which means mp has be to be positive and rt has to be positive.

answer C

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
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Hi Bunuel, here you have given that " ­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"

Is this a rule or an understanding?
Should i take it in general as - for a product of ODD NUMBERS - there must be a even number of negative among them?
How about for a product of EVEN NUMBERS then?


Bunuel
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.­
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SwethaReddyL
Hi Bunuel, here you have given that " ­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"

Is this a rule or an understanding?
Should i take it in general as - for a product of ODD NUMBERS - there must be a even number of negative among them?
How about for a product of EVEN NUMBERS then?


Don't overcomplicate it. Negative * negative = positive, so the product of an even number of negative numbers gives positive result.
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