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If x represents the sum of all the positive three-digit

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If x represents the sum of all the positive three-digit [#permalink] New post 13 Nov 2009, 19:35
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If x represents the sum of all the positive three-digit numbers that can be constructed using each of the distinct nonzero digits a, b, and c exactly once, what is the largest integer by which x must be divisible?

(A) 3
(B) 6
(C) 11
(D) 22
(E) 222
[Reveal] Spoiler: OA

Last edited by Bunuel on 30 Jul 2012, 03:29, edited 2 times in total.
Added the OA
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Re: this is what it has come down to [#permalink] New post 13 Nov 2009, 20:34
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rvthryet wrote:
If x represents the sum of all the positive three-digit numbers that can be constructed using each of the distinct nonzero digits a, b, and c exactly once, what is the largest integer by which x must be divisible?
(A) 3
(B) 6
(C) 11
(D) 22
(E) 222

I have never really understood the thinking behind this...
[Reveal] Spoiler:
OA E


Using THREE non-zero digits a,b,c only, we can construct 3!=6 numbers: abc, acb, bac, bca, cab, cba. Their sum will be:

x=(100a+10b+c)+(100a+10c+b)+(100b+10a+c)+(100b+10c+a)+(100c+10a+b)+(100c+10b+a)=
=200*(a+b+c)+20*(a+b+c)+2*(a+b+c)=
=222*(a+b+c)

Largest integer by which x MUST be divisible is 222.

Answer: E (222).
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Re: Testing number properties [#permalink] New post 03 Mar 2010, 03:26
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Maybe there is a faster way to do it but I did it like this:

How many ways can you arrange abc?
abc
acb
bac
bca
cab
cba

which are equivalent to:
100a + 10b + c
100a + 10c + b
100b + 10a + c
100b + 10c + a
100c + 10a + b
100c + 10b + a

if you add them all together you get 222a + 222b + 222c
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Re: If x represents the sum of all the positive three-digit [#permalink] New post 19 Sep 2013, 09:20
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Re: this is what it has come down to [#permalink] New post 13 Nov 2009, 19:40
where did this question come from wow I have like no idea where to begin I would assume 123 and 987 which are two combinations are both both divisible by 3 as the GCD so 3?
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Re: this is what it has come down to [#permalink] New post 13 Nov 2009, 20:47
Bunuel wrote:
rvthryet wrote:
If x represents the sum of all the positive three-digit numbers that can be constructed using each of the distinct
nonzero digits a, b, and c exactly once, what is the largest integer by which x must be divisible?
(A) 3
(B) 6
(C) 11
(D) 22
(E) 222

I have never really understood the thinking behind this...
[Reveal] Spoiler:
OA E


Using THREE non-zero digits a,b,c only, we can construct 3!=6 numbers: abc, acb, bac, bca, cab, cba. Their sum would be:

x=(100a+10b+c)+(100a+10c+b)+(100b+10a+c)+(100b+10c+a)+(100c+10a+b)+(100c+10b+a)=
=200*(a+b+c)+20*(a+b+c)+2*(a+b+c)=
=222*(a+b+c)

Largest integer by which x MUST be divisible is 222.

Answer: E (222).


Good explanation, exactly how I solved it. I love questions with elegant solutions like this. +1
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Re: this is what it has come down to [#permalink] New post 13 Nov 2009, 20:59
Expert's post
We can also solve this one without math using symmetry: hundreds, tens and units are symmetric, so sum can be written as (y)*111. We need to check that y is even. For example, for fixed a at hundred position, there is two bc,cb combinations. Therefore, a is included twice (even number of times) into sum of hundreds. So, it is 222

By the way, it is the first time when I add something after Bunuel :)
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Re: If x represents the sum of all the positive three-digit [#permalink] New post 31 Mar 2012, 02:27
To Bunuel,

I've gone thorugh ur notes for each Quant topic and I try to solve topic wise questions from gmatclub. Sometimes I'm not able to figure out how to start with the problem, or I should say how to apply the properties learned since, the techniques you give in your solution for a given problem are not there in properties or formulaes. What do you recommend ? I plan to give my Gmat nxt mnth end. This Tuesday, Veritas prep test I took I scored 600, Q44, verbal 33.

Kindly assist.
Thanks.
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Re: If x represents the sum of all the positive three-digit [#permalink] New post 30 Jul 2012, 03:26
.Though I was able to solve it (in a random way), but was unable to come up with a concrete approach.
@NickK kudos for that perfect one. This is how I did.....

The question asked for the largest divisor and thus we need to form 6 largest number that could be made using 3 distinct nonzero digits....987+978+897+879+798+789 = 5328...start from the largest number provided in the answer..222 divides 5328 completely hence is the answer
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Re: If x represents the sum of all the positive three-digit [#permalink] New post 01 Oct 2013, 05:40
ratinarace wrote:
.Though I was able to solve it (in a random way), but was unable to come up with a concrete approach.
@NickK kudos for that perfect one. This is how I did.....

The question asked for the largest divisor and thus we need to form 6 largest number that could be made using 3 distinct nonzero digits....987+978+897+879+798+789 = 5328...start from the largest number provided in the answer..222 divides 5328 completely hence is the answer


Agree, substitution works the best for 'must be true' problems.
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Re: this is what it has come down to [#permalink] New post 01 Oct 2013, 23:27
Bunuel wrote:
rvthryet wrote:
If x represents the sum of all the positive three-digit numbers that can be constructed using each of the distinct nonzero digits a, b, and c exactly once, what is the largest integer by which x must be divisible?
(A) 3
(B) 6
(C) 11
(D) 22
(E) 222

I have never really understood the thinking behind this...
[Reveal] Spoiler:
OA E


Using THREE non-zero digits a,b,c only, we can construct 3!=6 numbers: abc, acb, bac, bca, cab, cba. Their sum will be:

x=(100a+10b+c)+(100a+10c+b)+(100b+10a+c)+(100b+10c+a)+(100c+10a+b)+(100c+10b+a)=
=200*(a+b+c)+20*(a+b+c)+2*(a+b+c)=
=222*(a+b+c)

Largest integer by which x MUST be divisible is 222.

Answer: E (222).


Hi Bunuel,
Can you please explain me what will be the value of "x" in this question. If it were asked what is the value of x?

Thanks!
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Re: this is what it has come down to [#permalink] New post 02 Oct 2013, 02:12
Expert's post
shameekv wrote:
Bunuel wrote:
rvthryet wrote:
If x represents the sum of all the positive three-digit numbers that can be constructed using each of the distinct nonzero digits a, b, and c exactly once, what is the largest integer by which x must be divisible?
(A) 3
(B) 6
(C) 11
(D) 22
(E) 222

I have never really understood the thinking behind this...
[Reveal] Spoiler:
OA E


Using THREE non-zero digits a,b,c only, we can construct 3!=6 numbers: abc, acb, bac, bca, cab, cba. Their sum will be:

x=(100a+10b+c)+(100a+10c+b)+(100b+10a+c)+(100b+10c+a)+(100c+10a+b)+(100c+10b+a)=
=200*(a+b+c)+20*(a+b+c)+2*(a+b+c)=
=222*(a+b+c)

Largest integer by which x MUST be divisible is 222.

Answer: E (222).


Hi Bunuel,
Can you please explain me what will be the value of "x" in this question. If it were asked what is the value of x?

Thanks!


We cannot say what x is.

If a, b, and c, are 1, 2, and 3 respectively, then x = 123 + 132 + 213 + 231 + 312 + 321 = 1,332 = 6*222 (the least possible value of x).
...
If a, b, and c, are 7, 8, and 9 respectively, then x = 789 + 798 + 879 + 897 + 978 + 987 = 5,328 = 24*222 (the greatest possible value of x).

Hope it helps.
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NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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.


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Re: If x represents the sum of all the positive three-digit [#permalink] New post 02 Oct 2013, 02:27
Hi Bunuel,

Thanks for the clarification. I thought it is the sum of all such 3-digit numbers that have distinct numbers.

What in the case "x is the sum of all the 3-digit numbers that have distinct numbers". How do you calculate the value of x in such case. I tried many things but couldn't work it out.

I saw such type of question recently where x was required to be calculated but the digits could be repeated and that made it simple. But I couldn't figure out with this restriction. Could you please help me out on that?

Thanks,
Shameek
Re: If x represents the sum of all the positive three-digit   [#permalink] 02 Oct 2013, 02:27
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