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Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35

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Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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20 Feb 2012, 17:55
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64% (01:44) correct 36% (01:46) wrong based on 807 sessions

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Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35
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Joined: 02 Sep 2009
Posts: 51096
Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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20 Feb 2012, 20:41
42
25
Is x > 10^10 ?

(1) x > 2^34 --> we should compare $$2^{34}$$ and $$10^{10}$$ --> take the square root from both: we should compare $$2^{17}$$ and $$10^5=100,000$$. Now, $$2^{17}=2^{10}*2^7=1,024*128>100,000$$. Sufficient.

OR: $$2^{34}=(2^{10})^{3.4}=(1,024)^{3.4}>(10^3)^{3.4}=10^{(3*3.4)}=10^{10.2}>10^{10}$$.

(2) x = 2^35. Since we have the exact numerical value of x we should be able compare it to 10^10 and answer the question. It really doesn't matter whether 2^35>10^10, the main point is that we have sufficient information to get the answer. Sufficient.

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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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30 Jul 2012, 02:09
11
dvinoth86 wrote:
Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35

(1) Let's see if $$2^{34}>10^{10}$$.

$$2^{34}>2^{10}*5^{10}$$. Divide through by $$2^{10}$$, and we get $$2^{24}>5^{10}$$. Take the square root of both sides:
$$2^{12}>5^5$$. This we can compute quite easily, and we find that 1024*4=4096 > 625*5= 3125, TRUE.
Sufficient.

(2) We have already seen that (1) is sufficient, obviously (2) is also sufficient.
Just to play with powers, we can check that $$2^{35}>10^{10}$$:
Start again with $$2^{35}>2^{10}*5^{10}$$, divide through by $$2^{10}$$, then $$2^{25}>5^{10}$$. Now we can take the 5th order root of both sides and obtain $$2^5>5^2$$ or 32 > 25, TRUE.

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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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29 Jul 2012, 20:58
Bunuel rocks this is a very nice solution compared to the other ones I ve seen

Bunuel wrote:
Is x > 10^10 ?

(1) x > 2^34 --> we should compare $$2^{34}$$ and $$10^{10}$$ --> take the square root from both: we should compare $$2^{17}$$ and $$10^5=100,000$$. Now, $$2^{17}=2^{10}*2^7=1,024*128>100,000$$. Sufficient.

OR: $$2^{34}=(2^{10})^{3.4}=(1,024)^{3.4}>(10^3)^{3.4}=10^{(3*3.4)}=10^{10.2}>10^{10}$$.

(2) x = 2^35. Since we have the exact numerical value of x we should be able compare it to 10^10 and answer the question. It really doesn't matter whether 2^35>10^10, the main point is that we have sufficient information to get the answer. Sufficient.

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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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30 Jul 2012, 05:19
1
venmic wrote:
Bunuel rocks this is a very nice solution compared to the other ones I ve seen

Bunuel wrote:
Is x > 10^10 ?

(1) x > 2^34 --> we should compare $$2^{34}$$ and $$10^{10}$$ --> take the square root from both: we should compare $$2^{17}$$ and $$10^5=100,000$$. Now, $$2^{17}=2^{10}*2^7=1,024*128>100,000$$. Sufficient.

OR: $$2^{34}=(2^{10})^{3.4}=(1,024)^{3.4}>(10^3)^{3.4}=10^{(3*3.4)}=10^{10.2}>10^{10}$$.

(2) x = 2^35. Since we have the exact numerical value of x we should be able compare it to 10^10 and answer the question. It really doesn't matter whether 2^35>10^10, the main point is that we have sufficient information to get the answer. Sufficient.

Bunuel's logic for testing assumption (2) is excellent. In the present form of the question, one can use that $$2^{35}>2^{34}$$, so once (1) turns out sufficient and necessarily provides the info that $$2^{34}>10^{10}$$, testing (2) is very easy. Maybe, it would have been somehow more challenging to choose a smaller exponent in statement (2), like 33, with which direct comparison would have been not so straightforward, and a time saving approach would need similar logic to Bunuel's.
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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30 Jul 2012, 12:22
2
In my personal opinion, I just don't see this question following the style of the GMAT test writers. Unless, whoever wrote this can confirm that they recently saw a similar idea on the exam.

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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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04 Sep 2012, 02:43
1
Why would you need to compute anything in this problem?

Statement 1 gives us a minimum value of x. It doesn't matter if 10^10 is smaller or larger, it is sufficient to answer the question.
Statement 2 needs no computation either, which Bunuel already pointed out.
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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04 Sep 2012, 02:49
1
1
reklaw wrote:
Why would you need to compute anything in this problem?

Statement 1 gives us a minimum value of x. It doesn't matter if 10^10 is smaller or larger, it is sufficient to answer the question.
Statement 2 needs no computation either, which Bunuel already pointed out.

We do need to compare 10^10 and 2^34 in (1). Because if 2^34 were less than 10^10, then the statement wouldn't b sufficient. Consider this:

Is x>10?

(1) x>2. If x=5 then the answer is NO but if x=15, then the answer is YES. Not sufficient.

Hope it's clear.
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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04 Sep 2012, 02:54
Crystal.

Classic mistake, which is what is probably REALLY being tested, realised it when re-reading my post.

Thanks for response though.
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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16 Feb 2013, 13:19
Bunuel wrote:
Is x > 10^10 ?

(1) x > 2^34 --> we should compare $$2^{34}$$ and $$10^{10}$$ --> take the square root from both: we should compare $$2^{17}$$ and $$10^5=100,000$$. Now, $$2^{17}=2^{10}*2^7=1,024*128>100,000$$. Sufficient.

OR: $$2^{34}=(2^{10})^{3.4}=(1,024)^{3.4}>(10^3)^{3.4}=10^{(3*3.4)}=10^{10.2}>10^{10}$$.

(2) x = 2^35. Since we have the exact numerical value of x we should be able compare it to 10^10 and answer the question. It really doesn't matter whether 2^35>10^10, the main point is that we have sufficient information to get the answer. Sufficient.

Bunuel,

I solved it a different way- would you mind checking my approach?

I restructured the qstem to is x =,> 2^11 * 5^11?

(1) x > 2^34

- x has 2^11 therefore 2^35 - 2^11 = 2^24
- estimated 2^2 to be 5 and divided 24 by 2 and got 5^12
- x = 2^11 * 5^12 -------- SUFFICIENT

(2) X = 2^35

- SUFFICIENT

Is this approach correct?
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Re: Is x > 10^10  [#permalink]

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17 Feb 2013, 23:35
1
A very coarse method but I would do this problem by log.

F.S.1 gives logx > 34 log2 = 34*0.3 = 10.2(approx). As problem statement is asking about whether x>10^10, it boils down to logx>10. Thus suficient.

F.S.2 anyways gives the value of logx = 35*0.3. Again logx>10.
Sufficient.

D.

Not the best method but a pretty quick one. I don't think it is a 700+ level question.
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Re: Is x > 10^10  [#permalink]

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18 Feb 2013, 01:22
vinaymimani wrote:
A very coarse method but I would do this problem by log.

F.S.1 gives logx > 34 log2 = 34*0.3 = 10.2(approx). As problem statement is asking about whether x>10^10, it boils down to logx>10. Thus suficient.

F.S.2 anyways gives the value of logx = 35*0.3. Again logx>10.
Sufficient.

D.

Not the best method but pretty quick. I don't think it is a 700+ level question.

Good one. Can you please share some source/ tutorial of this method?
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Re: Is x > 10^10  [#permalink]

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18 Feb 2013, 01:25
greatps24 wrote:
vinaymimani wrote:
A very coarse method but I would do this problem by log.

F.S.1 gives logx > 34 log2 = 34*0.3 = 10.2(approx). As problem statement is asking about whether x>10^10, it boils down to logx>10. Thus suficient.

F.S.2 anyways gives the value of logx = 35*0.3. Again logx>10.
Sufficient.

D.

Not the best method but pretty quick. I don't think it is a 700+ level question.

Good one. Can you please share some source/ tutorial of this method?

No tutorial as such. Just that they gave a power of 10 in this question and also 2^something. So it just struck me. Worked in this question, might not work always!
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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07 Jul 2013, 23:54
Bumping for review and further discussion*. Get a kudos point for an alternative solution!

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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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08 Jul 2013, 14:25
1
dvinoth86 wrote:
Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35

hi,

statement 2 is clear we are able to calculate...HENCE SUFFICIENT
for statement 1
2^34=2^10*8^8===>(1
10^10=2^10*5^10===>(2

actually we have to compare 2^34..and 10^10
both of them have 2^10 common...so we have to compare actually 8^8 and 5^10...

5^10=(8-3)^8*25=25*(8-3)^8
lets divide 5^10..with 8^8..==>25*((8-3)/8)^8==>clearly we can see that 25 is multiplied to a very small no.(as bracket number is less than 1,and it has been raised to power 8)==>end resul will be less than 1...==>this proves 8^8 is greater than 5^10....hence...2^34>10^10==>sufficient.

both statements are sufficient..hence D
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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31 Jul 2014, 13:15
dvinoth86 wrote:
Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35

(2) is 1 number, so it is sufficient
(1) compare 2^34 > 10^10 ?
-> 2^10 * 2^24 > 2^10 * 5^10
-> 2^24 > 5^10
-> 2^12 > 5^5 ( square root)
-> 2^10 * 2^2 > 5^3 * 5^2
-> 1028*4 > 125*25
-> 4112 > 3125 ( correct)

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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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08 Dec 2014, 00:34
1
Bunuel wrote:
Is x > 10^10 ?

(1) x > 2^34 --> we should compare $$2^{34}$$ and $$10^{10}$$ --> take the square root from both: we should compare $$2^{17}$$ and $$10^5=100,000$$. Now, $$2^{17}=2^{10}*2^7=1,024*128>100,000$$. Sufficient.

OR: $$2^{34}=(2^{10})^{3.4}=(1,024)^{3.4}>(10^3)^{3.4}=10^{(3*3.4)}=10^{10.2}>10^{10}$$.

(2) x = 2^35. Since we have the exact numerical value of x we should be able compare it to 10^10 and answer the question. It really doesn't matter whether 2^35>10^10, the main point is that we have sufficient information to get the answer. Sufficient.

Oh Bunuel, you are always awesome. For me, your approach is always faster than Manhanttan's.
Highly recommend GMAT club for all GMAT learner!!!
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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30 Dec 2015, 11:44
dvinoth86 wrote:
Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35

whenever there is a 10 (or its multiples) involved, i use log.

is x > 10^10
or log x > 10 log 10
or log x > 10 ?

1) x > 2^34
log x > 34*log 2
log x > 10.23 (sufficient)

2) has to be sufficient
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Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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30 Dec 2015, 22:26
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35

In case of inequality questions, it is important to note that the conditions are sufficient if the range of the question includes the range of the conditions.
There is 1 variable (x) in the original condition. In order to match the number of variables and the number of equations, we need 1 equation. Since the condition 1) and 2) each has 1 equation, there is high chance D is going to be the answer.

In the case of the condition 1), if we do the calculation, we get 10^10<10*(10^3)^3=10*(1000)^3<16*(1024)^3=(2^4)(2^10)^3=2^34. Since the range of the question includes the range of the conditions, the condition 1) is sufficient.

In the case of the condition 2), if x=2^35, the answer can always be either ‘yes’ or ‘no’. Therefore, the condition is sufficient, and the correct answer is D.

For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously, there may be cases where the answer is A, B, C or E.
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Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35  [#permalink]

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24 Mar 2016, 02:01
dvinoth86 wrote:
Is x > 10^10 ?

(1) x > 2^34
(2) x = 2^35

My working is just a tad different.

Statement 2, enough
Statement 1,
x > 10^10
x > 2^10.5^10

So x > 2^34
x > 2^10.2^24

Now, my thinking was 5 is 2.5 times more than 2, so 5^10 will be closer to 2^20 but w/o working i cant say higher or lower , whereas 2^21 > 5^10 (definite as its 1 more than double), we have 2^24. So sufficient.
I know its not perfect but saved time for me, of course Bunuel's method is flawless !!.
Re: Is x > 10^10 ? (1) x > 2^34 (2) x = 2^35 &nbs [#permalink] 24 Mar 2016, 02:01

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