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# What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b

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Math Expert
Joined: 02 Sep 2009
Posts: 49206
What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b  [#permalink]

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06 Oct 2017, 04:49
2
5
00:00

Difficulty:

75% (hard)

Question Stats:

53% (01:25) correct 47% (02:19) wrong based on 123 sessions

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CHALLENGE QUESTIONS

What will be the remainder when $$13^7 + 14^7 + 15^7 + 16^7$$ is divided by 58?

A. 0
B. 1
C. 28
D. 30
E. 57

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Math Expert
Joined: 02 Aug 2009
Posts: 6786
Re: What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b  [#permalink]

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06 Oct 2017, 06:41
5
7
Bunuel wrote:

CHALLENGE QUESTIONS

What will be the remainder when $$13^7 + 14^7 + 15^7 + 16^7$$ is divided by 58?

A. 0
B. 1
C. 28
D. 30
E. 57

hi..

Here we have to remember that $$a^n+b^n$$ is always div by a+b when n is ODD

so 58 should tell you that 58=2*29 and the numbers in equation also add up to 29 - 13+16 and 14+15
$$13^7 + 14^7 + 15^7 + 16^7= (13^7+16^7)+(14^7+15^7)$$

two things
1) the entire sum is $$Odd^7+Even^7+Odd^7+Even^7$$.. here total will be EVEN
2) now $$13^7+16^7$$ will be div by 13+16=29 and similarly $$14^7+15^7.$$.

so the the EQUATION is div by 2 and also by 29..

thus remainder will be 0

ans A
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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##### General Discussion
Intern
Joined: 12 Mar 2017
Posts: 4
Location: India
WE: General Management (Energy and Utilities)
Re: What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b  [#permalink]

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01 Jan 2018, 19:56
1
1
The numbers can be added as = (13+14+15+16)^7 =(58)^7 {followed x^n+y^n=(x+y)^n}

Above divided by 58 would give u reminder 0.

Plz let me know in case this approach is correct.
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Joined: 20 Feb 2017
Posts: 88
Location: United States
Re: What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b  [#permalink]

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01 Jan 2018, 20:24
Pallabi89 wrote:
The numbers can be added as = (13+14+15+16)^7 =(58)^7 {followed x^n+y^n=(x+y)^n}

Above divided by 58 would give u reminder 0.

Plz let me know in case this approach is correct.

x^n + y^n is not equal to (x+y)^n
e.g.
(x+y)^2 = (x+y) X (x+y) = x^2+ y^2 + xy +xy = x^2 + y^2 + 2xy
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Math Expert
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Posts: 6786
Re: What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b  [#permalink]

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01 Jan 2018, 21:16
Pallabi89 wrote:
The numbers can be added as = (13+14+15+16)^7 =(58)^7 {followed x^n+y^n=(x+y)^n}

Above divided by 58 would give u reminder 0.

Plz let me know in case this approach is correct.

Hi...

You cannot take a case in isolation and generalized..

Firstly x^n+y^n is not equal to (x+y)^n unless n is 1 or one of x andy is 0..
There may some more cases here.

Now incase you meant for checking divisibility ONLY..
Check whether n is odd or even..
If odd x^n+y^n is div by x+y otherwise not..

Example 2^2+4^2 is not div by 2+4 or 6

So be careful
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

GMAT online Tutor

Re: What will be the remainder when 13^7 + 14^7 + 15^7 + 16^7 is divided b &nbs [#permalink] 01 Jan 2018, 21:16
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