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Senior Manager  B
Status: No dream is too large, no dreamer is too small
Joined: 14 Jul 2010
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Is the integer x divisible by 36? (1) x is divisible by 12  [#permalink]

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1 00:00

Difficulty:   5% (low)

Question Stats: 88% (00:30) correct 13% (00:27) wrong based on 79 sessions

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Is the integer x divisible by 36 ?

(1) x is divisible by 12.
(2) x is divisible by 9.

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/is-the-intege ... 67497.html

My approach was as follows
(1)24, 48 is divisible by 12 but not by 36 so NS
(2) 27, 81 is divisible by 9 but noty 36. So NS

considering two: the integer which is divisible by 12 and 9 is multiple 3 and 36 is multiple 3. So any digit divisible 12 and 9 is also divisible by 36.

Please help with good approach.

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Re: Is the integer x divisible by 36? (1) x is divisible by 12  [#permalink]

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Prime factors of $$36 = 2^2*3^2$$

So if x is divided by a number whose factors at least comprise of all the prime factors of 36; i.e. two 2's and two 3's then x will be divisible by 36.

1.Prime factors of 12 = 2^2*3
So; only two 2's and one 3. We require 2 two's and two 3's for the number to be divisible by 36.
Not Sufficient.

2.Prime factors of 9 = 3^2
So; only two 3's. We require 2 two's and two 3's for the number to be divisible by 36.
Not Sufficient.

Combining both;
x is divisible by; 2^2*3*3^2
The factors comprise of at least two 2's and two 3's. Must be divisible by 36.
Sufficient.

Ans: "C"
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GMAT 1: 760 Q50 V44 Re: Is the integer x divisible by 36? (1) x is divisible by 12  [#permalink]

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Mate, you can download my flashcards and take a look at slides 81-84. All the approaches to find GCF and LCM are there. Hope it helps.

Link: my-comprehensive-quant-flashcards-109836.html

Solving the question:
Always find the prime factors, as fluke showed. Then, remember that GCF is formed by the shared prime factors.

The 36's prime factors box has: 2, 2, 3, 3

(1) 12's prime box has 2, 2, 3. A 3 is missing, so not sufficient

(2) 9's prime box has 3, 3. Not sufficient as well (two 2's missing)

If you combine them, you will have two shared 2's and two shared 3's, which are the same as the prime factors of 36. So, both are sufficient. A number that is divisible by 9 and by 12 will also be divisible by 36.

Cheers
Manager  Joined: 07 Jun 2010
Posts: 81
Re: Is the integer x divisible by 36? (1) x is divisible by 12  [#permalink]

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Find whether 36 is factor of X......

Break down 36 to prime factors....2*2*3*3

If 36 is factor of x, then the 2*2*3*3 are factors (equivalent)

This is true if we know other factors that also exhaust the prime factors.

A. 12 is a factor of x. 2*3*2 are the prime factors. This covers all the factors of 36 except for the second 3. We don't have proof that x has a second 3 as a factors so A is insufficient

B. 9 is a prime factors. 3*3 are the prime factors. This covers only 3*3 and doesn't tell us whether 2*2 are also factors. Insufficient.

Both A&B tells us that we have 3*3 and 3*2*2 as factors.

The maximum number of a certain prime factor need to come from one of the factors, as it does. Both 3's come from the 9, both 2s come from the 12. Sufficient C
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Re: Is the integer x divisible by 36? (1) x is divisible by 12  [#permalink]

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Is the integer x divisible by 36 ?

(1) x is divisible by 12. If x=12, then the answer is NO but if x=36, then the answer is YES. Not sufficient.

(2) x is divisible by 9. If x=9, then the answer is NO but if x=36, then the answer is YES. Not sufficient.

(1)+(2) From above it follows that x must be divisible by the least common multiple of 12 and 9, which is 36. Sufficient.

Answer: C.

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/is-the-intege ... 67497.html

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

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_________________ Re: Is the integer x divisible by 36? (1) x is divisible by 12   [#permalink] 16 Aug 2017, 09:23
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# Is the integer x divisible by 36? (1) x is divisible by 12

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