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# If [z] denotes the least integer greater

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e-GMAT Representative
Joined: 04 Jan 2015
Posts: 2942
If [z] denotes the least integer greater  [#permalink]

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24 May 2017, 11:50
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Difficulty:

75% (hard)

Question Stats:

49% (01:50) correct 51% (01:47) wrong based on 237 sessions

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Q.

If [z] denotes the least integer greater than or equal to z and [$$z^2$$] = 2, which of the following could be the value of [z]?

I. 2
II. 1
III. -2

A. I only
B. II only
C. III only
D. I and II only
E. II and III only

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Joined: 24 Apr 2016
Posts: 327
If [z] denotes the least integer greater  [#permalink]

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24 May 2017, 14:13
1
$$[z^2] = 2$$ means that

$$1<z^2\leq{2}$$

Now, Taking Square Root of both the sides.

If Z is positive, then

$$1<z\leq{\sqrt{2}}$$

then [z] = 2

If Z is negative, then

$$-1>z\geq{-\sqrt{2}}$$

then [z] = -1

Math Expert
Joined: 02 Sep 2009
Posts: 56277
Re: If [z] denotes the least integer greater than or equal to z and [z2] =  [#permalink]

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25 May 2017, 14:05
1
2
niteshwaghray wrote:
If [z] denotes the least integer greater than or equal to z and [$$z^2$$] = 2, which of the following could be the value of [z]?

I) 2
II) 1
III) -2

A. I only
B. II only
C. III only
D. I and II only
E. II and III only

Given function rounds up a number to the nearest integer. For example, [1.3] = 2, because 2 is the least integer greater than or equal to 1.3.

[$$z^2$$] = 2;

$$1 < z^2 \leq 2$$;

$$1 <|z| \leq \sqrt{2}$$ ($$\sqrt{2} \approx 1.4$$).

$$1 < z \leq \sqrt{2}$$ or $$-1 > z \geq \sqrt{2}$$

[z] can be 2 (if $$1 < z \leq \sqrt{2}$$) or -1 (if $$-1 > z \geq \sqrt{2}$$).

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Joined: 04 Jan 2015
Posts: 2942
Re: If [z] denotes the least integer greater  [#permalink]

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31 May 2017, 06:09
3
1
1

Official Solution

Given:

• The function [z]
• $$[z^2] = 2$$

To find: Can [z] be {2, 1, -2}?

Approach:

• To find which values of [z] are possible and which are not, we need to first know the range of possible values of z. Once we know what z can be, we’ll be able to find what [z] can be.

We’ll get an idea of the possible values of z from the fact that $$[z^2] = 2$$

Working Out:

• $$[z^2] = 2$$

• This means the least integer that is greater than or equal to $$z^2$$ is 2.

• We can write: $$1 < z^2 ≤ 2$$

• The above inequality contains 2 inequalities: $$z^2 > 1$$ AND $$z^2 ≤ 2$$
So now, we’ll solve these inequalities one by one, and then find the values of z that satisfy both these inequalities

• Solving $$z^2 > 1$$

• $$z^2 – 1 > 0$$

• $$(z+1)(z-1) > 0$$

This means, $$z < - 1$$ or $$z > 1$$ . . . (1)

• Solving $$z^2 ≤ 2$$

• $$z^2 – 2 ≤ 0$$

• $$(z + √2)(z-√2) ≤ 0$$

That is, $$-√2 ≤ z ≤ √2$$ . . . (2)

Combining (1) and (2):

Combining them to find their overlap zones and finding those values of z that satisfy both the inequalities

• So, either $$-√2 ≤ z < -1$$ or $$1 < z ≤ √2$$

• Either $$-√2 ≤ z < -1$$

• $$-1.4 ≤ z < -1$$

• In this case, $$[z] = -1$$

• Or $$1 < z ≤ √2$$

• $$1 < z ≤ 1.4$$

• $$[z] = 2$$
Thus, we see that [z] is either equal to -1 or equal to 2. Out of the 3 given values, only value I (which is 2) is therefore possible.

Looking at the answer choices, we see that the correct answer is Option A

Thanks,
Saquib
Quant Expert
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If [z] denotes the least integer greater than or equal to z and [z^2]  [#permalink]

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05 Mar 2018, 07:01
If [z] denotes the least integer greater than or equal to z and [z^2] = 2, which of the following could be the value of [z]?

I. 2
II. 1
III. -2

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) II and III only
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Math Expert
Joined: 02 Aug 2009
Posts: 7764
Re: If [z] denotes the least integer greater than or equal to z and [z^2]  [#permalink]

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05 Mar 2018, 07:25
2
1
itisSheldon wrote:
If [z] denotes the least integer greater than or equal to z and [z^2] = 2, which of the following could be the value of [z]?

I. 2
II. 1
III. -2

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) II and III only

Good question...
if [z^2] =2, $$z^2$$ lies between 2 and 3
therefore z lies between $$\sqrt{2}=1.4$$ and $$\sqrt{3}=1.7$$ or between $$-\sqrt{2}=-1.4$$ and $$-\sqrt{3}=-1.7$$ if z is negative..
so when z is positive it lies between 1.4 and 1.7 and the NEXT greater integer is 2 so [z]=2
but when z is negative it lies between -1.4 and -1.7 and the NEXT greater integer is -1 so [z]=-1.. Be careful here and do not take -2

Only 2 is given
ans A
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Math Expert
Joined: 02 Sep 2009
Posts: 56277
Re: If [z] denotes the least integer greater  [#permalink]

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05 Mar 2018, 07:30
itisSheldon wrote:
If [z] denotes the least integer greater than or equal to z and [z^2] = 2, which of the following could be the value of [z]?

I. 2
II. 1
III. -2

(A) I only

(B) II only

(C) III only

(D) I and II only

(E) II and III only

Merging topics. Please search before posting. Thank you.
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Joined: 07 Mar 2019
Posts: 29
Re: If [z] denotes the least integer greater  [#permalink]

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02 Jul 2019, 09:03
I don't understand, where does the z > 1 and z < -1 come from?
Re: If [z] denotes the least integer greater   [#permalink] 02 Jul 2019, 09:03
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