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Retired Moderator Joined: 07 Jun 2014
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GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
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If k is a multiple of 24 but not a multiple of 16, which of [#permalink]
Expert's post 00:00

Question Stats: 53% (01:29) correct 46% (01:09) wrong based on 39 sessions
If k is a multiple of 24 but not a multiple of 16, which of the following cannot be an integer?

(A) $$\frac{k}{8}$$
(B) $$\frac{k}{9}$$
(C) $$\frac{k}{32}$$
(D) $$\frac{k}{36}$$
(E) $$\frac{k}{81}$$
[Reveal] Spoiler: OA

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Sandy
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Try our free Online GRE Test Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 175

Kudos [?]: 3037  , given: 394

Re: If k is a multiple of 24 but not a multiple of 16, which of [#permalink]
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Expert's post
Explanation

If k is a multiple of 24, it contains the prime factors of 24: 2, 2, 2, and 3. (It could also contain other prime factors, but the only ones for certain are the prime factors contained in 24.)

If k were a multiple of 16, it would contain the prime factors of 16: 2, 2, 2, and 2.

Thus, if k is a multiple of 24 but not of 16, k must contain 2, 2, and 2, but not a fourth 2 (otherwise, it would be a multiple of 16).

Thus: k definitely has 2, 2, 2, and 3. It could have any other prime factors (including more 3’s) except for more 2’s.

An answer choice in which the denominator contains more than three 2’s would guarantee a non-integer result. Only choice (C) works. Since k has fewer 2’s than 32, can never be an integer.

Alternatively, list multiples of 24 for k: 24, 48, 72, 96, 120, 144, 168, etc. Then, eliminate multiples of 16 from this list: 24, , 72, , 120, , 168, etc.

A pattern emerges: k = (an odd integer) $$\times 24$$:

(A) can be an integer, for example when $$k = 24.$$

(B) can be an integer, for example when $$k = 72.$$

(C) is correct by process of elimination.

(D) can be an integer, for example when $$k = 72.$$

(E) can be an integer, for example when $$k = 81 \times 24.$$
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Sandy
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Re: If k is a multiple of 24 but not a multiple of 16, which of [#permalink]
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Intern  Joined: 07 May 2020
Posts: 20
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Kudos [?]: 13 , given: 72

Re: If k is a multiple of 24 but not a multiple of 16, which of [#permalink]
sandy wrote:
If k is a multiple of 24 but not a multiple of 16, which of the following cannot be an integer?

(A) $$\frac{k}{8}$$
(B) $$\frac{k}{9}$$
(C) $$\frac{k}{32}$$
(D) $$\frac{k}{36}$$
(E) $$\frac{k}{81}$$

If K is not a multiple of 16, then K won't be multiple of any 16x
You can test some numbers, but if you have no time, just scan the answer choices and see that only option C has a denominator 2*16, thus dividing K by 32 won't give us an integer Re: If k is a multiple of 24 but not a multiple of 16, which of   [#permalink] 07 Jun 2020, 07:16
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