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# If 2^x*7^y = z, what is the value of z ? (1) x − y = 1 (2) 2^x = 8

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Math Expert
Joined: 02 Sep 2009
Posts: 58453
If 2^x*7^y = z, what is the value of z ? (1) x − y = 1 (2) 2^x = 8  [#permalink]

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05 Mar 2019, 04:50
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Difficulty:

5% (low)

Question Stats:

96% (00:59) correct 4% (00:50) wrong based on 48 sessions

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If $$2^x*7^y = z$$, what is the value of z ?

(1) $$x − y = 1$$

(2) $$2^x = 8$$

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Joined: 31 Oct 2013
Posts: 1464
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
If 2^x*7^y = z, what is the value of z ? (1) x − y = 1 (2) 2^x = 8  [#permalink]

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05 Mar 2019, 05:20
Bunuel wrote:
If $$2^x*7^y = z$$, what is the value of z ?

(1) $$x − y = 1$$

(2) $$2^x = 8$$

Statement 1: x - y = 1. x=y + 1.

$$2^{y + 1} 7^y = z$$

$$2^y * 7^y*2 = z$$

$$(14)^y 2 = z.$$

No information about y. NOT sufficient.

Statement 2: $$2^x = 8$$. $$2^x = 2^3$$. x =3. No information about y. NOT sufficient.

Combining :

x - y = 1

3 - y = 1

y = 2.

So, x = 3 and y = 2. Now we can find out the total value.

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Re: If 2^x*7^y = z, what is the value of z ? (1) x − y = 1 (2) 2^x = 8  [#permalink]

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05 Mar 2019, 11:02
Bunuel wrote:
If $$2^x*7^y = z$$, what is the value of z ?

(1) $$x − y = 1$$

(2) $$2^x = 8$$

#1
x-y=1
means x & y are consective values . but x & y are not know in suffieint
#2
2^x=8
or say x = 3
in sufficeint as y not know
so 1&2
x=3 and y = 2
sufficient
IMO C
Re: If 2^x*7^y = z, what is the value of z ? (1) x − y = 1 (2) 2^x = 8   [#permalink] 05 Mar 2019, 11:02
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