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# If multiplying a certain number by itself 7 times yields y and 2y = 43

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Math Expert
Joined: 02 Sep 2009
Posts: 51121
If multiplying a certain number by itself 7 times yields y and 2y = 43  [#permalink]

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03 Jan 2017, 01:37
00:00

Difficulty:

15% (low)

Question Stats:

78% (01:40) correct 22% (01:57) wrong based on 153 sessions

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If multiplying a certain number by itself 7 times yields y and 2y = 4374, what is the number?

A. 2187
B. 624
C. 17
D. 3
E. 2

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Re: If multiplying a certain number by itself 7 times yields y and 2y = 43  [#permalink]

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03 Jan 2017, 06:38
x^7 = y
2(x^7) = 4374
x^7 = 2187

x = 3

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Re: If multiplying a certain number by itself 7 times yields y and 2y = 43  [#permalink]

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03 Jan 2017, 07:51
2
Bunuel wrote:
If multiplying a certain number by itself 7 times yields y and 2y = 4374, what is the number?

A. 2187
B. 624
C. 17
D. 3
E. 2

2y = 4374

Or,$$y = 2187$$

So, we can say x^7 will be 2187

Since the units digit is 7 , the units digit of x must be 3

So, 3^7 = 2187

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Joined: 01 Nov 2017
Posts: 29
If multiplying a certain number by itself 7 times yields y and 2y = 43  [#permalink]

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27 Jun 2018, 07:22
1) 2y = 4374 => y = 2,187
2) realized that 3^7 or 2^7 would likely be <= to 2187 and 17^7 would be huge
3) Broke up 3^7 so I had 9x9x9x3 = 81x9x3 = 729x3 = ~2100

So D
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Re: If multiplying a certain number by itself 7 times yields y and 2y = 43  [#permalink]

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02 Jul 2018, 09:04
Bunuel wrote:
If multiplying a certain number by itself 7 times yields y and 2y = 4374, what is the number?

A. 2187
B. 624
C. 17
D. 3
E. 2

We can let the number = n and create the equation:

n^7 = y

We also have:

2y = 4374

y = 2187

Thus, we have:

n^7 = 2187

Let’s check answer choices to determine a possible value for n. Since n^7 is odd, we can eliminate all the even choices, such as B and E. Next, we see that 17 is too large a value for n: 10^7 is 10000000 and 17^7 is even larger than that. Since 17 (and every value greater than 17) is eliminated, the only possible value is n = 3.

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Re: If multiplying a certain number by itself 7 times yields y and 2y = 43 &nbs [#permalink] 02 Jul 2018, 09:04
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