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Bunuel
Is f(n) > f(n−1)?

(1) n = 8
(2) f(n) = n−1

Asked: Is f(n) > f(n−1)?

(1) n = 8
Since f(n) is unknown
NOT SUFFICIENT

(2) f(n) = n−1
f(n-1) = n-2
n-1>n-2
f(n)>f(n-1)
SUFFICIENT

IMO B
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Bunuel
Is f(n) > f(n−1)?

(1) n = 8
(2) f(n) = n−1

Analyzing the question:
You can think of this question as asking us whether f(n) is a strictly increasing function. The type of functions that can increase then decrease are quadratic or not linear. If f(n) is linear it must be strictly increasing or decreasing.

Statement 1: Tells us nothing about the function. Insufficient.
Statement 2: f(n) is linear, and the slope is 1. Since the slope is greater than 0, f(n) always increases as n increases. Therefore f(n) > f(n-1) for all n. Sufficient.

Ans: B
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iamsiddharthkapoor
(1) Since we don't know what the function is we can't comment whether or not f(n)>f(n-1)
Thus, insufficient.

(2) f(n)= n-1
So, f(n-1)= (n-1)-1=n-2
=> f(n)>f(n-1)
Thus, sufficient.

Therefore, the answer is option B.


while compluting 2nd equation, it is not sufficient when n have negative value. why is it not taken into consideration?
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iamsiddharthkapoor
(1) Since we don't know what the function is we can't comment whether or not f(n)>f(n-1)
Thus, insufficient.

(2) f(n)= n-1
So, f(n-1)= (n-1)-1=n-2
=> f(n)>f(n-1)
Thus, sufficient.

Therefore, the answer is option B.


while compluting 2nd equation, it is not sufficient when n have negative value. why is it not taken into consideration?


Even if n is negative, S2 would hold true.

Let's take n to be -3.

According to S2:
f(n) = n-1
f (n-1) = n-1-1 = n-2

The question is asking whether n-1>n-2.

Substituting -3 for n
-3-1 > -3-2
-4 > -5

Therefore, S2 is sufficient
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