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Re: 132^5-2(132^4)+6(132^3)-3(132)/65 [#permalink]
GreenlightTestPrep wrote:
lazyashell wrote:
\(\frac{132^5-2(132^4)+6(132^3)-3(132)}{65}\), what is the remainder?

A.40
B.42
C.44
D.47
E.54


Unless I'm completely missing something, I believe we need modular arithmetic to solve this question.
If this is the case, then the question is out of scope for the GRE

Maybe I'm approaching my question wrong, but this seems very familiar to one I got on an actual test about a week ago:
5^1/3+95^1/3+207^1/3=x^1/3; what is x?

I had, and still have, absolutely no idea how to solve it.
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Re: 132^5-2(132^4)+6(132^3)-3(132)/65 [#permalink]
Expert Reply
DFXR wrote:
GreenlightTestPrep wrote:
lazyashell wrote:
\(\frac{132^5-2(132^4)+6(132^3)-3(132)}{65}\), what is the remainder?

A.40
B.42
C.44
D.47
E.54


Unless I'm completely missing something, I believe we need modular arithmetic to solve this question.
If this is the case, then the question is out of scope for the GRE

Maybe I'm approaching my question wrong, but this seems very familiar to one I got on an actual test about a week ago:
5^1/3+95^1/3+207^1/3=x^1/3; what is x?

I had, and still have, absolutely no idea how to solve it.


Please Sir

read the comment above provided by the tutor

Regards
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Re: 132^5-2(132^4)+6(132^3)-3(132)/65 [#permalink]
2
1
I think we should have much simpler solution, but please let me try.

#STEP1 : simplify numerator.
132^5 - 2(132^4 ) + 6(132^3)-3(132)

Focus on left 2 elements.
132^5 - 2(132 ^ 4 ) =(132^4)(132 - 2) = 132^4(130)
130 is 2 x 65 so, remainder of 132^4(130 ) should be zero, so we can ignore.

#STEP2 calculate right 2 elements of numerator.
This was not fun part me , but..

6(132^3)-3(132) = 132(6 x 132^2 -3 ) = 132(17424 x 6-3) = 130 x (17424 x 6 -3 ) + 2 x (17424 x 6 -3 ) = 130 x 104541 + 2 x 104541
We know that result of above multiplication will be end XX....2 , so we can guess that answer should be B or D.
But I could not determine which was correct , so I needed to calculate rest .

We can ignore 130 x 104541 part, rest is 2 x 104541 = 209082

#STEP3 Calculate remainder.
It's enough simple to calculate for me.
209082 / 65 = 3216 with 42 , so answer is B) , 42
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Re: 132^5-2(132^4)+6(132^3)-3(132)/65 [#permalink]
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Remainder when 132 is divided by 65 is 2, 4 for 132^2, 8 for 132^5 and so on. So we just need to solve the numerator by replacing 132 with 2.
2^5 - 2(2^4) + 6(2^3) - 3(2) = 42.
I don't know if this approach is mathematically correct or not but it yields the correct answer.
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Re: 132^5-2(132^4)+6(132^3)-3(132)/65 [#permalink]
megha08ks93 wrote:
Remainder when 132 is divided by 65 is 2, 4 for 132^2, 8 for 132^5 and so on. So we just need to solve the numerator by replacing 132 with 2.
2^5 - 2(2^4) + 6(2^3) - 3(2) = 42.
I don't know if this approach is mathematically correct or not but it yields the correct answer.



I think your solution seems to be correct, and much simpler, just for one note, I think you wanted to write 8 for 132^3 not 8 for 132^5 ?
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132^5-2(132^4)+6(132^3)-3(132)/65 [#permalink]
1
We need to find the remainder of \(132^5 − 2*132^4 + 6*132^3 −3*132\) by 65

We solve these problems by using Binomial Theorem, where we split the number into two parts, one part is a multiple of the divisor(65 or 130) and a big number, other part is a small number.

=> \(132^{5}\) = \((130 + 2)^{5}\)

Watch this video to MASTER BINOMIAL Theorem

Now, when we expand this expression then all the terms except the last term will be a multiple of 130 or 65.
=> All terms except the last term will give 0 as remainder then divided by 65
=> Problem is reduced to what is the remainder when the last term is divided by 65
=> What is the remainder when \(5C5 * 130^0 * 2^{5}\) is divided by 65 = Remainder of \(2^{5}\) by 65 = 32

=> Remainder of \(132^5 \) by 65 = remainder of 32 by 65 = 32

Remainder of 2*132^4 by 65 = Remainder of 2*2^4 by 65 = Remainder of 32 by 65 = 32
Remainder of 6*132^3 by 65 = Remainder of 6*2^3 by 65 = Remainder of 48 by 65 = 48
Remainder of 3*132 by 65 = Remainder of 3*(130 + 2) by 65 = Remainder of 3*2 by 65 = 6

=> Total Remainder = 32 - 32 + 48 - 6 = 42

So, Answer will be B
Hope it helps!

Watch following video to MASTER Remainders by 2, 3, 5, 9, 10 and Binomial Theorem

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