how to compare

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clock60: Legendary Member; Posts: 759; Joined: Mon Apr 26, 2010 10:15 amFollowed by: 3 members; Thanked: 85 times

by clock60 » Fri Jul 30, 2010 12:13 pm

hi guys
can somebody help me with problems like that:
how to compare
10^10 and 2^34
or
31^11 and 17^14
or
2^40 and 3^28

seriously it is not a joke and not for practice purposes, i faced very similar in MG, and solve the problem wrong.

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Source: Beat The GMAT — Problem Solving | Fri Jul 30, 2010 12:13 pm

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Fri Jul 30, 2010 2:44 pm

clock60 wrote:hi guys
can somebody help me with problems like that:
how to compare
10^10 and 2^34
or
31^11 and 17^14
or
2^40 and 3^28

seriously it is not a joke and not for practice purposes, i faced very similar in MG, and solve the problem wrong.

I'm not sure what you mean by "compare"

For example, to we compare 2 and 6, we could say that 6 is 4 greater than 2, or we could say that 6 is 3 times 2.
Can you provide an actual GMAT question?

Brent Hanneson - Creator of GMATPrepNow.com

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clock60: Legendary Member; Posts: 759; Joined: Mon Apr 26, 2010 10:15 amFollowed by: 3 members; Thanked: 85 times

by clock60 » Sat Jul 31, 2010 3:14 am

hi Brent
thank you for reply.
below is problem. i know that it is DS problem, so must be posted in DS section. but i am interested in the approach here

Is x > 10^10 ?
(1) x > 2^34
(2)(2) x = 2^35
oa is D the source manhattan CAT

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Sat Jul 31, 2010 3:48 am

clock60 wrote:hi Brent
thank you for reply.
below is problem. i know that it is DS problem, so must be posted in DS section. but i am interested in the approach here

Is x > 10^10 ?
(1) x > 2^34
(2)(2) x = 2^35
oa is D the source manhattan CAT

(1) 2^34 = 2^ (3.4 Ã— 10) = (2^3.4) ^10, and since a rough estimation could make us believe that 2^3.4 is greater than 10, hence anything more than 2^34 is got to be greater than 10^10. Sufficient

(2) The explanation above in (1) helps us call this too sufficient.

[spoiler]D[/spoiler]

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

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clock60: Legendary Member; Posts: 759; Joined: Mon Apr 26, 2010 10:15 amFollowed by: 3 members; Thanked: 85 times

by clock60 » Sat Jul 31, 2010 4:28 am

hi sanju09
your solving is too smart for me,( i am sure that it is valid)
i want to replicate with my own words

2^34=2^(3,4*10)=(2^3,4)^10 we need to compare with 10^10

2^3,4=(10+x) where x is any positive number

so (10+x)^10>10^10
and it happens that 2^34>10^10
i see it is genious

but how you guess that 2^3.4>10
it is really 10.556
anyway many many thanks

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Sat Jul 31, 2010 4:42 am

clock60 wrote:hi sanju09
your solving is too smart for me,( i am sure that it is valid)
i want to replicate with my own words

2^34=2^(3,4*10)=(2^3,4)^10 we need to compare with 10^10

2^3,4=(10+x) where x is any positive number

so (10+x)^10>10^10
and it happens that 2^34>10^10
i see it is genious

but how you guess that 2^3.4>10
it is really 10.556
anyway many many thanks

2^3.4 = 4^1.7, which is faintly less than the square of 4, not enough that could take 16 below 10 in any case, it's a sheer ballpark figure to make persuaded about something else rather than the exact value.

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

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