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QOTD#15 In the equation above, x is an integer with 3

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Joined: 07 Jun 2014
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QOTD#15 In the equation above, x is an integer with 3 [#permalink]  16 Nov 2016, 13:06
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Question Stats:

75% (01:46) correct 25% (00:00) wrong based on 4 sessions
$$\frac{xz}{y}=420$$

In the equation above, x is an integer with 3 distinct prime factors, and y is a positive integer with no prime factors. If z is a positive, non-prime number, what is one possible value of z?

Drill 4
Question: 6
Page: 293

[Reveal] Spoiler: OA
4, 6, 10, and 14

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GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4710
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 91

Kudos [?]: 1612 [0], given: 375

Re: QOTD#15 In the equation above, x is an integer with 3 [#permalink]  16 Nov 2016, 13:12
Expert's post
Explanation

Don’t forget that you can use your on-screen calculator. There’s only one positive integer with no prime factors, the number 1. Therefore, y = 1, and xz = 420. Create a prime factor tree to get the prime factors of 420: 2, 2, 3, 5, and 7. Pick 3 distinct values from that list, such as 2, 3, and 5, and multiply them to find one possible value of x. One example is 2 × 3 × 5 = 30, or one
possible value for x. If 30z = 420, then z = 14. Confirm that 14 is not prime, then enter it in the field. If you chose 2, 3, 7, then x is 42 and z is 10 and also correct, and so on.
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Re: QOTD#15 In the equation above, x is an integer with 3 [#permalink]  25 Nov 2016, 17:56
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Expert's post
sandy wrote:
$$\frac{xz}{y}=420$$

In the equation above, x is an integer with 3 distinct prime factors, and y is a positive integer with no prime factors. If z is a positive, non-prime number, what is one possible value of z?

[Reveal] Spoiler: OA
4, 6, 10, and 14

y is a positive integer with no prime factors
That should strike you as an odd statement.
There's only one such number: 1
So, we already know that y = 1

So, we have (xz)/1 = 420
This means that xz = 420

When we find the prime factorization of 420, we get: 420 = (2)(2)(3)(5)(7)
In other words, xz = (2)(2)(3)(5)(7)

GIVEN: x is an integer with 3 distinct prime factors
So, for example, x could equal (2)(3)(5) [aka 30]
Or x could equal (2)(3)(7) [aka 42]
Or x could equal (3)(5)(7) [aka 105]
Or x could equal (2)(5)(7) [aka 70]

If x = 30, then z = 14
If x = 42, then z = 10
If x = 105, then z = 4
If x = 70, then z = 6

So, the possible values of z are: 4, 6, 10, and 14

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Re: QOTD#15 In the equation above, x is an integer with 3   [#permalink] 25 Nov 2016, 17:56
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