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MT1302
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gmatophobia
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I think the answer is C . KarishmaB chetan2u Can you please share your explanations ?
gmatophobia

Gangadhar111990
­In an experiment, the rate at which a certain bacterium grows is G. If G is a function of time t, such that
G= \( xt^3 \) +\( yt^2 \) + z , where x, y, and z are constants and t > 0. Is there a value of t for which G is negative?

(1) x > y > z
(2) z > 0­
­
G(t) = \( xt^3 \) +\( yt^2 \) + z

Statement 1

(1) x > y > z

Inference: x lies to the right of y which lies to the right of z on a number line. 

Attachment:
Screenshot 2024-03-23 204850.png

We do not know the position of zero.

Case 1: zero lies to the left of \(z\)

In this case, G(t) is always positive.

Is there a value of t for which G is negative? ⇒ No

Case 2: zero lies to the right of \(x\)

In this case, G(t) is always negative.

Is there a value of \(t\) for which G is negative? ⇒ Yes

Attachment:
Screenshot 2024-03-23 205007.png

As we are getting two answers, the statement alone is not sufficient to answer the question. 
 ­
Statement 2

(2) z > 0­

In this case, zero lies to the left of z. Hence, x, y, and z are always positive.

Therefore the value of G(t) is always positive.

Is there a value of t for which G is negative? ⇒ No

 
Attachment:
Screenshot 2024-03-23 205350.png

Option B­
­
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MT1302
­In an experiment, the rate at which a certain bacterium grows is G. If G is a function of time t, such that
\(  G=xt^3 +yt^2 + z \) , where x, y, and z are constants and t > 0. Is there a value of t for which G is negative?

(1) x > y > z
(2) z > 0­
­
(1) x > y > z

All 3 could be negative which would make \(  G=xt^3 +yt^2 + z \) negative for all positive values of t.

(2) z > 0­

 x and y could still be negative which would make \(  G=xt^3 +yt^2 + z \) negative for some values of t. 

Using both, all three are positive which means \(  G=xt^3 +yt^2 + z \) will be positive for all positive values of t. 

Answer (C)
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MT1302
­In an experiment, the rate at which a certain bacterium grows is G. If G is a function of time t, such that \(G = xt^3 + yt^2 + z\), where x, y, and z are constants and t > 0. Is there a value of t for which G is negative?

(1) x > y > z
(2) z > 0­

"Is there a value of..." suggests that if I have at least one value of t for which G is negative, though we may have other values that turn G positive, it's enough to have a suffficient statement, not that I must have all negative values.
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