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If n and k are integers whose product is 400, which of the

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If n and k are integers whose product is 400, which of the  [#permalink]

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New post 30 Jun 2012, 00:46
1
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A
B
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D
E

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Question Stats:

58% (01:37) correct 42% (01:28) wrong based on 373 sessions

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If n and k are integers whose product is 400, which of the following statements must be true?

A. n + k > 0
B. n is not equal to k.
C. Either n or k is a multiple of 10.
D. If n is even, then k is odd.
E. If n is odd, then k is even.

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Re: If n and k are integers whose product is 400, which of the f  [#permalink]

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New post 30 Jun 2012, 02:22
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If n and k are integers whose product is 400, whcih of the following statements must be true?

Note that the question is: "whcih of the following must be true?"

Given: \(nk=400\)

For the product of two integers to be even at least one integer must be even.

A. n+k>0 --> not necessarily true: \(nk=(-20)*(-20)=400\);
B. n does not equal k --> not necessarily true: \(nk=20*20=400\);
C. Either n or k is a multiple of 10 --> not necessarily true: \(nk=16*25=400\).
D. If n is even, then k is odd --> not necessarily true, \(n\) can be even and \(k\) be even too --> \(nk=20*20=400\);
E. If n is odd, then k is even --> this must be true, if one of the factors is odd (\(n\)) the second one (\(k\)) must be even for their product to be even.

Answer: E.

Hope it's clear.
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Re: If n and k are integers whose product is 400, which of the  [#permalink]

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New post 01 Jul 2012, 20:58
Ohh..this one was really fun..got screwed up btw D and E. Didn't read between the lines. Thanks for explaining Bunuel.
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Re: If n and k are integers whose product is 400, which of the  [#permalink]

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New post 05 May 2015, 23:19
Bunuel wrote:
If n and k are integers whose product is 400, whcih of the following statements must be true?

Note that the question is: "whcih of the following must be true?"

Given: \(nk=400\)

For the product of two integers to be even at least one integer must be even.

A. n+k>0 --> not necessarily true: \(nk=(-20)*(-20)=400\);
B. n does not equal k --> not necessarily true: \(nk=20*20=400\);
C. Either n or k is a multiple of 10 --> not necessarily true: \(nk=16*25=400\).
D. If n is even, then k is odd --> not necessarily true, \(n\) can be even and \(k\) be even too --> \(nk=20*20=400\);
E. If n is odd, then k is even --> this must be true, if one of the factors is odd (\(n\)) the second one (\(k\)) must be even for their product to be even.

Answer: E.

Hope it's clear.



I need just to know that if n is odd, k is even. this is enough to tick e. no need explanation more.
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Re: If n and k are integers whose product is 400, which of the  [#permalink]

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New post 12 May 2015, 01:38
Bunuel wrote:
If n and k are integers whose product is 400, whcih of the following statements must be true?

Note that the question is: "whcih of the following must be true?"

Given: \(nk=400\)

For the product of two integers to be even at least one integer must be even.

A. n+k>0 --> not necessarily true: \(nk=(-20)*(-20)=400\);
B. n does not equal k --> not necessarily true: \(nk=20*20=400\);
C. Either n or k is a multiple of 10 --> not necessarily true: \(nk=16*25=400\).
D. If n is even, then k is odd --> not necessarily true, \(n\) can be even and \(k\) be even too --> \(nk=20*20=400\);
E. If n is odd, then k is even --> this must be true, if one of the factors is odd (\(n\)) the second one (\(k\)) must be even for their product to be even.

Answer: E.

Hope it's clear.


in the test room, we can not find 25x16=400 easily. so, if we see E, if n is odd then k is even

tick choice E. that is done.
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Re: If n and k are integers whose product is 400, which of the  [#permalink]

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New post 12 May 2015, 03:40
If n and k are integers whose product is 400, which of the following statements must be true?

A.n + k > 0 n and k should have the same sign, but that means that they can also both be negative
B.n is not equal to k. 20 x 20 = 400[i]
C. Either n or k is a multiple of 10. [i]25 x 16 = 400

D. If n is even, then k is odd. k can also be even since even x even will be even
E. If n is odd, then k is even. k must be even since odd x even = even
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Re: If n and k are integers whose product is 400, which of the  [#permalink]

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New post 17 May 2018, 17:02
Stiv wrote:
If n and k are integers whose product is 400, which of the following statements must be true?

A. n + k > 0
B. n is not equal to k.
C. Either n or k is a multiple of 10.
D. If n is even, then k is odd.
E. If n is odd, then k is even.


Since an even product must contain at least 1 even number in the multiplication, if n is odd, then k must be even.

If you had difficulty differentiating between choices D and E, consider the wording. Choice D states that if we are given that n is even, then k must be odd, which is not necessarily true, because k could be even. Take n = 20 and k = 20 for instance (which also eliminates answer choice B). However, Choice E states that if we are given that n is odd, then k must be even. This is a true statement, because the product nk is even.

Answer: E
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Re: If n and k are integers whose product is 400, which of the  [#permalink]

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New post 14 Sep 2018, 00:29
we should begin with 400=2^2*5^2*2^2

from this we see that all condition except choice E can be correct but must not be correct.
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Re: If n and k are integers whose product is 400, which of the &nbs [#permalink] 14 Sep 2018, 00:29
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