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M19-35

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M19-35 [#permalink]

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New post 16 Sep 2014, 00:07
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Question Stats:

92% (00:34) correct 8% (00:46) wrong based on 144 sessions

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Re M19-35 [#permalink]

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New post 16 Sep 2014, 00:07
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Official Solution:

Which of the following numbers is equal to \(8!\) ?

A. 38910
B. 39340
C. 39980
D. 40320
E. 40450

Backsolve. \(8!\) has to be divisible by 3. Choices B, C, and E are out for this reason. \(8!\) has to be divisible by 4. Hence choice A is out. The only viable option is choice D.

Answer: D
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Re: M19-35 [#permalink]

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New post 02 Feb 2016, 22:37
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Bunuel wrote:
Official Solution:

Which of the following numbers is equal to \(8!\) ?

A. 38910
B. 39340
C. 39980
D. 40320
E. 40450

Backsolve. \(8!\) has to be divisible by 3. Choices B, C, and E are out for this reason. \(8!\) has to be divisible by 4. Hence choice A is out. The only viable option is choice D.

Answer: D



no need to backsolve.
no need to check the divisibility.
how about this=>
since 6!=720
8!=720*8*7=> 720*56=> 72*56*10
here the tens digit must must be 2
hence option D
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Re: M19-35 [#permalink]

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New post 05 Jul 2016, 10:45
How about checking divisibility with 8.(Since 8! will have 8)
Backsolve. 8! has to be divisible by 8

Only (D) satisfies .

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Re: M19-35 [#permalink]

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New post 08 Apr 2017, 00:52
Hi Bunuel,

I did by looking for divisibilty to 8. Is it correct also?

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Re: M19-35 [#permalink]

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New post 08 Apr 2017, 03:16

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Re: M19-35 [#permalink]

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New post 08 Sep 2017, 06:12
stonecold wrote:
Bunuel wrote:
Official Solution:

Which of the following numbers is equal to \(8!\) ?

A. 38910
B. 39340
C. 39980
D. 40320
E. 40450

Backsolve. \(8!\) has to be divisible by 3. Choices B, C, and E are out for this reason. \(8!\) has to be divisible by 4. Hence choice A is out. The only viable option is choice D.

Answer: D



no need to backsolve.
no need to check the divisibility.
how about this=>
since 6!=720
8!=720*8*7=> 720*56=> 72*56*10
here the tens digit must must be 2
hence option D


yes, I also looked for tenth digit unit of answer choices and then recognized they're totally different. So just leave out 5*2=10, multiply unit digit of 7*8 = 56*6=6*4*3=2, only choice D

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M19-35 [#permalink]

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New post 30 Sep 2017, 02:07
Bunuel wrote:
dyg wrote:
Hi Bunuel,

I did by looking for divisibilty to 8. Is it correct also?


Yes. A number is divisible by 8 if the number formed by the last three digits is divisible by 8. Since only 320 (D) is divisible by 8 then it must be correct.


Hi Bunuel, Does this work with all numbers? Like is a number divisible 4 if its last 3 digits are divisible by 4? Is it a rule? Thanks.

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Re: M19-35 [#permalink]

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New post 30 Sep 2017, 03:31
1
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Expert's post
aashishagarwal2 wrote:
Bunuel wrote:
dyg wrote:
Hi Bunuel,

I did by looking for divisibilty to 8. Is it correct also?


Yes. A number is divisible by 8 if the number formed by the last three digits is divisible by 8. Since only 320 (D) is divisible by 8 then it must be correct.


Hi Bunuel, Does this work with all numbers? Like is a number divisible 4 if its last 3 digits are divisible by 4? Is it a rule? Thanks.


A number is divisible by 2 if the last digit is divisible by 2.
A number is divisible by 4 if the last 2 digits are divisible by 4.
A number is divisible by 8 if the last 3 digits are divisible by 8.
...
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 135988 [1], given: 12719

Re: M19-35   [#permalink] 30 Sep 2017, 03:31
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