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# If a, b, and c are consecutive integers and 0 < a < b < c, is the prod

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Joined: 01 Sep 2010
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Kudos [?]: 9510 [0], given: 1203

If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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27 Jul 2017, 07:18
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47% (04:00) correct 53% (01:49) wrong based on 167 sessions

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If a, b, and c are consecutive integers and 0 < a < b < c, is the product abc a multiple of 8 ?

(1) The product ac is even.

(2) The product bc is a multiple of 4.
[Reveal] Spoiler: OA

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Kudos [?]: 9510 [0], given: 1203

Math Expert
Joined: 02 Aug 2009
Posts: 5349

Kudos [?]: 6128 [0], given: 121

If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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27 Jul 2017, 07:31
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carcass wrote:
If a, b, and c are consecutive integers and 0 < a < b < c, is the product abc a multiple of 8 ?

(1) The product ac is even.

(2) The product bc is a multiple of 4.

hi,

If a, b, and c are consecutive integers and 0 < a < b < c, is the product abc a multiple of 8
TWO cases..
A) a and c are even AND b is ODD.... abc will always be multiple of 8 or rather 24.. ans will be YES
B) a and c are ODD and b is even.. if b is multiple of 8.. YES otherwise NO

lets see the statements
(1) The product ac is even.
this MEANS a and c are even..
falls under category A above..
always YES
sufficient

(2) The product bc is a multiple of 4

either b is multiple of 4, ans can be YES or NO case B
OR c is multiple of 4, ans will be YES.. case A
insuff

A
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Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 6128 [0], given: 121

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Re: If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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27 Jul 2017, 07:34

Statement 1:
ac is even -> a and c are even and b is odd, minimum possible values of abc is 2*3*4.
Sufficient

Statement 2:
bc multiple of 4 --> b can be 4.. c can be 5.... so a can be 3, which gives abc=60
not sufficient

Kudos [?]: 3 [0], given: 12

Intern
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Re: If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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01 Dec 2017, 14:58
I don't get why a and c are even AND b is ODD.... abc will always be multiple of 8 or rather 24, could you explain me please

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Re: If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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01 Dec 2017, 19:38
analuisa wrote:
I don't get why a and c are even AND b is ODD.... abc will always be multiple of 8 or rather 24, could you explain me please

Hi analuisa

as the numbers are consecutive, so $$a$$, $$b$$, $$c$$ can take two options -

Case 1: Even, Odd, Even OR

Case 2: Odd, Even, Odd

Statement 1: as $$ac$$ is even, so it has to be Case 1

Now let $$a=2k$$ (even number) so $$b=2k+1$$ and $$c=2k+2=2(k+1)$$, where $$k$$ is any number greater than $$0$$ (because $$0<a<b<c$$)

Hence $$ac=2k*2(k+1)=4k(k+1)$$

so if $$k$$ is odd then $$k+1=even$$, hence $$4k(k+1)$$ will be a multiple of $$8$$

if $$k$$ is even then $$4k$$ will be a multiple of $$8$$. Therefore $$abc$$ is a multiple of $$8$$ because $$ac$$ is a multiple of $$8$$. Sufficient

Statement 2: $$bc$$ is a multiple of $$4$$. so it could be multiple of $$8$$ such as $$16,24,32$$ etc. or it could not be a multiple of $$8$$ such as $$20, 28$$ etc.. Insufficient

Option A

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Manager
Joined: 31 Jul 2017
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Kudos [?]: 17 [0], given: 333

Re: If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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01 Dec 2017, 20:29
carcass wrote:
If a, b, and c are consecutive integers and 0 < a < b < c, is the product abc a multiple of 8 ?

(1) The product ac is even.

(2) The product bc is a multiple of 4.

The Best would be to plug in by numbers.

Let b = n, a = n-1, c = n+1

Stmnt 1: ac = even, $$n^2$$ - 1 =even, Here n can be only a odd number starting from 3,5,7,9,11 etc.. So abc will be Divisible by 8.
Stmnt 2: n(n+1) = 4m.. Here, n can be 3,4,7,8,9,11,13,14.. etc. when n = 3, abc Divisible by 8 but n= 4, abc not divisible by 8.

Hope this Helps.

Kudos [?]: 17 [0], given: 333

Math Expert
Joined: 02 Aug 2009
Posts: 5349

Kudos [?]: 6128 [0], given: 121

Re: If a, b, and c are consecutive integers and 0 < a < b < c, is the prod [#permalink]

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01 Dec 2017, 20:48
analuisa wrote:
I don't get why a and c are even AND b is ODD.... abc will always be multiple of 8 or rather 24, could you explain me please

Hi...
Three consecutive integers and two even means even, odd, even...
Now since three are consecutive, one of them would surely be a MULTIPLE of 3.
Two of them even means one will be MULTIPLE of 2 and other will be MULTIPLE of atleast 4 so product will be MULTIPLE of atleast 3*2*4=24
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 6128 [0], given: 121

Re: If a, b, and c are consecutive integers and 0 < a < b < c, is the prod   [#permalink] 01 Dec 2017, 20:48
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