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What is the remainder obtained when 63^25 is divided by 16?

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Manager
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What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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29 Oct 2018, 05:32
2
4
00:00

Difficulty:

35% (medium)

Question Stats:

62% (01:02) correct 38% (00:44) wrong based on 92 sessions

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What is the remainder obtained when $$63^{25}$$ is divided by 16?

A. -1
B. 0
C. 5
D. 10
E. 15
Manager
Joined: 14 Jun 2018
Posts: 223
Re: What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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29 Oct 2018, 06:22
$$\frac{65^(25)}{16} = -1^(25) = -1$$

Remainder = 16-1 = 15
Intern
Joined: 13 Mar 2018
Posts: 24
GPA: 3.12
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Re: What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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07 Nov 2018, 09:34
1
pandeyashwin wrote:
$$\frac{65^(25)}{16} = -1^(25) = -1$$

Remainder = 16-1 = 15

Please explain why we cannot consider Option A= -1.

As per me, this question should have two answers= -1 & 15. ( NEGATIVE & POSITIVE REMAINDERS )

Manager
Joined: 14 Jun 2018
Posts: 223
Re: What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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07 Nov 2018, 18:38
AnupamKT wrote:
pandeyashwin wrote:
$$\frac{65^(25)}{16} = -1^(25) = -1$$

Remainder = 16-1 = 15

Please explain why we cannot consider Option A= -1.

As per me, this question should have two answers= -1 & 15. ( NEGATIVE & POSITIVE REMAINDERS )

Manager
Joined: 03 Mar 2017
Posts: 211
What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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07 Nov 2018, 19:06
AnupamKT wrote:
pandeyashwin wrote:
$$\frac{65^(25)}{16} = -1^(25) = -1$$

Remainder = 16-1 = 15

Please explain why we cannot consider Option A= -1.

As per me, this question should have two answers= -1 & 15. ( NEGATIVE & POSITIVE REMAINDERS )

63^25 can be written as ((64-1)^25)/16

64 is divisible by 16. what is left is -1^25 which turns out to be -1.

Always make numerator in such a manner that it gets divided by denominator.

But remainder can never by negative hence -1+16 (denominator here) gives 15.

Therefore E.
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Re: What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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07 Nov 2018, 19:20
AnupamKT wrote:
pandeyashwin wrote:
$$\frac{65^(25)}{16} = -1^(25) = -1$$

Remainder = 16-1 = 15

Please explain why we cannot consider Option A= -1.

As per me, this question should have two answers= -1 & 15. ( NEGATIVE & POSITIVE REMAINDERS )

Remainder is ALWAYS positive. If you ever get a negative remainder. Just add the divisor to the negative remainder.

Ex: What's the remainder when 31 is divided by 16.

32 is completely divisible by 16. Hence for 31 we get a negative remainder of -1. Adding the divisor, we get -1+16 = 15.

Hope it's clear

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Intern
Joined: 02 Sep 2016
Posts: 9
Re: What is the remainder obtained when 63^25 is divided by 16?  [#permalink]

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07 Nov 2018, 19:59
Unit place cyclicity of 3 -> 3,9,7,1
and Unit place cyclicity of 7 -> 7,9,3,1.

Now,
(63)^25 / 16 = (3 * 3 * 7)^25 /16
=> (3 * 3 * 7)/16 => 63/16
=> remainder as 15.
Re: What is the remainder obtained when 63^25 is divided by 16? &nbs [#permalink] 07 Nov 2018, 19:59
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