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If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the

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If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 06 Nov 2014, 09:18
1
5
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A
B
C
D
E

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Tough and Tricky questions: Exponents.



If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the value of xy?

(1) z = 20
(2) x = –1

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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 06 Nov 2014, 13:24
1
Statement 1 can be simplified to achieve 2^x*5^y*z=2*5^(-5)
if z=2^2*5
then 2^x*5^y = 2^-1*5^4
From this we see x=-1, 5=4, thus we can find xy.

Statement 2 is not enough as value of y would depend on value of z which is still unkown.
5^y*z=2^2*5^-5.
Insufficient to find answer
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 06 Nov 2014, 19:59
2^x*5^y*z= 64 * 10^-5 = 2^6*2^-5*5^-5 = 2^1*5^-5

Statement 1 : z = 20
We can write 2^1*5^-5 = 2^-1*5^-6 *2^2*5^1 = 2^-1*5^-6*20
Since z =20, then x = -1 and y=-6
Sufficient

Statement 2: x = –1
Since we don't know the value of z, we cannot determine the value of 5^y. Therefore, Statement 2 is insufficient

Answer should be A
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 06 Nov 2014, 22:55
2^x 5^y z = .00064

statement 1 -

z=20 clearly sufficient.

statement 2 -

x=-1

5^y * z = 128/10^5
5^y * z = 2^2 5^-5

y=-5 and x= -1

xy=5. sufficient.

OA is D.

Bunuel, please confirm.
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 19 Dec 2014, 05:18
1
If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the value of xy?

(1) z = 20
(2) x = –1

Here is my version.
1) if z=20 ==> 2^(x)*5^(y)=(0.00064/20)=0.000032 ==> 2^(x)*5^(y)=32*10^(-6) ==> 2^(x)*5^(y)=2^(5)*(2*5)^(-6) ==>x=-1 and y=6 ==>xy=-6
2) We know x=-1 but nothing is said about z. Hence not sufficient. Hope it is clear
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 20 Dec 2014, 15:39
navkaran wrote:
Statement 1 can be simplified to achieve 2^x*5^y*z=2*5^(-5)
if z=2^2*5
then 2^x*5^y = 2^-1*5^4
From this we see x=-1, 5=4, thus we can find xy.

Statement 2 is not enough as value of y would depend on value of z which is still unkown.
5^y*z=2^2*5^-5.
Insufficient to find answer


Hi navkaran:

Can you please elaborate how you go from "..if z=2^2*5" to "..then 2^x*5^y = 2^-1*5^4". My reason is that I am getting a different value for y only, just want to make sure my methods aren't incorrect. Thank you.
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 14 Jan 2015, 21:39
The statement asks 2^x . 5^y. z = 0.00064 which can be translated into prime factors as

Statement 1: 2^x . 5^y. z = 2^6 . 10^ -6 = 2^0 . 5^ -6
comparing both the parts we get x= 0 & y=-6 so xy= 0
sufficient.

Statement 2: 5^y . z = 0.000128 which means y & z can take any values. not sufficient.

Therefore A.
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 03 Mar 2017, 14:04
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JusTLucK04 wrote:
If x, y, and z are integers and 2x 5yz = 6.4 × 106, what is the value of xy?
(1) z = 20
(2) x = 9




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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 04 Mar 2017, 06:24
(2^x)(5^y)z = 64 x 10^-5
St 1: z = 20. therefore
(2^x)(5^y) = 32 x 10^-6 = 2^5 x (5 x 2)^-6 = 2^-1 x 5^-6.
Hence, x = -1 and y = -6. xy = 6. ANSWER

St 2: x = 9. no idea about z. INSUFFICIENT.

Option A
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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 30 Aug 2018, 23:24

Please someone explain Statement 2:

statement 2 -

x=-1
substitute x in the given equation.
2^-1 * 5^y * z = 64* 10^-5
5^y * z = 2^2 5^-5

y=-5 and x= -1

xy=5. sufficient.

why cannot the OA be D

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Re: If x, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the  [#permalink]

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New post 30 Aug 2018, 23:43
SonGoku wrote:

Please someone explain Statement 2:

statement 2 -

x=-1
substitute x in the given equation.
2^-1 * 5^y * z = 64* 10^-5
5^y * z = 2^2 5^-5

y=-5 and x= -1

xy=5. sufficient.

why cannot the OA be D

Bunuel nightblade354


From \(5^y * z = 2^2 5^{-5}\) we cannot conclude that y = -5. What if say y = -6 and z = 20? Or y = -7 and z = 100? ...
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New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
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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, y, and z are integers and (2^x)*(5^y)*z = 0.00064, what is the &nbs [#permalink] 30 Aug 2018, 23:43
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