Exponents

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zagcollins: Master | Next Rank: 500 Posts; Posts: 167; Joined: Wed Jun 11, 2008 10:58 pmFollowed by: 1 member; Thanked: 2 times

by zagcollins » Sun Jul 20, 2008 7:36 am

Which of the following is equal to 2^12-2^6/2^6-2^3?

A.2^6+2^3
B.2^6-2^3
C.2^9
D.2^3
E.2

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Source: Beat The GMAT — Problem Solving | Sun Jul 20, 2008 7:36 am

pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Sun Jul 20, 2008 9:24 am

You should write parenthesis, it could be confusing.

2^12 - 2^6 = (2^6)^2 - (2^3)^2 = (2^6+2^3)(2^6-2^3)
You put it in your numerator and delete both 2^6-2^3

So it is 2^6+2^3

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mbaapplicant2008: Senior | Next Rank: 100 Posts; Posts: 42; Joined: Thu Oct 30, 2008 1:21 am

by mbaapplicant2008 » Fri Oct 31, 2008 12:07 am

Yes, the answer is B

MBA Applicant

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Fri Oct 31, 2008 5:03 am

I think this problem has been solved in the forum.

2^12 - 2 ^ 6 = (2^6+2^3) (2^6-2^3) [
a ^ 2 - b ^ 2 = (a+b) (a-b)]

2^6-2^3 cancels out in the NUMERATOR AND DENOMINATOR leaving

2^6+2^3 as the answer

Hope this helps!

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divs: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Nov 01, 2008 5:15 am; Location: Bangalore

by divs » Mon Nov 03, 2008 7:38 am

:!: ...still a beginner.... But can someone tell me why it cant be solved this way ?!

2^6 ( 2^2 -1 ) / 2^3 ( 2^2 -1 )

= 2^6 / 2^3

= 2^3 :!:

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jnellaz: Master | Next Rank: 500 Posts; Posts: 114; Joined: Mon Oct 20, 2008 7:03 pmFollowed by: 5 members; Thanked: 4 times

by jnellaz » Mon Nov 03, 2008 10:51 am

I got the same answer as divs. Can any explain why this is wrong?

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amitabhprasad: Master | Next Rank: 500 Posts; Posts: 259; Joined: Thu Jan 18, 2007 8:30 pm; Thanked: 16 times

by amitabhprasad » Mon Nov 03, 2008 11:13 am

I think you guys are trying to multiple exponents with same base. While exponents are added/subtracted with same base not multipled

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Hope700: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Tue Oct 28, 2008 2:58 pm; Thanked: 1 times

Explaining

by Hope700 » Mon Nov 03, 2008 11:19 am

divs wrote::!: ...still a beginner.... But can someone tell me why it cant be solved this way ?!

2^6 ( 2^2 -1 ) / 2^3 ( 2^2 -1 )

= 2^6 / 2^3

= 2^3 :!:

(2^6 ) (2^2) is not the same as 2^12

Remember that when you multiply integers with exponents , the exponents add together , they do NOT multiply themselves
Therefore

(2^6)(2^2) = 2^8 is not the same as

(2^6)(2^6) = 2^12 Be careful this GMAT Creators know about this easy mistakes

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jnellaz: Master | Next Rank: 500 Posts; Posts: 114; Joined: Mon Oct 20, 2008 7:03 pmFollowed by: 5 members; Thanked: 4 times

by jnellaz » Mon Nov 03, 2008 1:43 pm

Thanks Hope700!

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divs: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Nov 01, 2008 5:15 am; Location: Bangalore

by divs » Mon Nov 03, 2008 8:18 pm

sheeezz !!! Thanks Hope700.... !! that was a stupid goof up.... :roll:

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vishubn: Legendary Member; Posts: 574; Joined: Sun Jun 01, 2008 8:48 am; Location: Bangalore; Thanked: 28 times

by vishubn » Tue Nov 04, 2008 5:39 am

Ya straight forward

But again !! u never know the trap ! or the mistake we make

Vishu

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Hope700: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Tue Oct 28, 2008 2:58 pm; Thanked: 1 times

by Hope700 » Tue Nov 04, 2008 8:39 am

Well it happens sometimes

Have a good day all

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