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TAGS: Active Member  Joined: 07 Jan 2018
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If x = 2^7^4 - 2^7^0, what is the largest [#permalink]
1
KUDOS 00:00

Question Stats: 63% (00:36) correct 36% (00:18) wrong based on 22 sessions
If $$x = 2^7^4 - 2^7^0$$, what is the largest prime factor of x?

A)2
B)3
C)5
D)7
E)11

src:orbit test prep
[Reveal] Spoiler: OA GRE Instructor Joined: 10 Apr 2015
Posts: 3876
Followers: 159

Kudos [?]: 4683  , given: 70

Re: If x = 2^7^4 - 2^7^0, what is the largest [#permalink]
1
KUDOS
Expert's post
amorphous wrote:
If $$x = 2^7^4 - 2^7^0$$, what is the largest prime factor of x?

A)2
B)3
C)5
D)7
E)11

Given: x = 2^74 - 2^70
Factor 2^70 from right side to get: x = 2^70(2^4 - 1)
Evaluate to get: x = 2^70(16 - 1)
Simplify to get: x = (2^70)(15)
Factor 15 to get: x = (2^70)(3)(5)

So, there are 3 different prime factors: 2, 3 and 5
The greatest prime is 5

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com
If you enjoy my solutions, you'll like my GRE prep course. Manager  Joined: 06 Jun 2018
Posts: 94
Followers: 2

Kudos [?]: 80 , given: 0

Re: If x = 2^7^4 - 2^7^0, what is the largest [#permalink]
amorphous wrote:
If $$x = 2^7^4 - 2^7^0$$, what is the largest prime factor of x?

A)2
B)3
C)5
D)7
E)11

src:orbit test prep

Given,

$$x = 2^7^4 - 2^7^0$$

$$x= 2^{70}(2^4 - 1)$$

$$x = 2^{70} 15$$

$$x = 2^{70}*5*3.$$

So, 5 is the largest prime of x. Re: If x = 2^7^4 - 2^7^0, what is the largest   [#permalink] 07 Sep 2018, 19:44
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