| View previous topic :: View next topic |
| Author |
Message |
ajmoney09
Rising GMAT Star
Joined: 25 May 2008
Posts: 55
Thanks given: 0
Thanked 0 times in 0 posts
|
 Posted: Wed Jul 16, 2008 9:39 pm Post subject: Question Exponents |
 |
|
No idea.
I divided by two to end up with 2^x - 2^x-1 = 3^13
Don't know what to do after that....OA is D
Help,
Thanks,
AJ. |
|
| Back to top |
|
 |
|
|
sudhir3127
Moderator
Joined: 07 Jul 2008
Posts: 724
Thanks given: 0
Thanked 56 times in 52 posts
Location: INDIA
Target GMAT Score: 700+
|
| Posted: Wed Jul 16, 2008 10:56 pm Post subject: |
|
|
| can u post the question .. i am not being able to see the picture. |
|
| Back to top |
|
|
parallel_chase
GMAT Destroyer!
Joined: 20 Jun 2007
Posts: 949
Thanks given: 15
Thanked 101 times in 94 posts
Target GMAT Score: V50
|
| Posted: Thu Jul 17, 2008 2:36 am Post subject: Re: Question Exponents |
|
|
| ajmoney09 wrote: |
No idea.
I divided by two to end up with 2^x - 2^x-1 = 3^13
Don't know what to do after that....OA is D
Help,
Thanks,
AJ. |
2^x - 2^x-2 = 3(2^13)
2^x - 2^x/2^2
2^x(1-1/2^2) => 2^x (3/4)
=> 3(2^x-2) = 3 (2^13)
therefore x =15
Let me know if you have any questions. |
|
| Back to top |
|
|
pepeprepa
GMAT Destroyer!
Joined: 08 Jul 2008
Posts: 660
Thanks given: 10
Thanked 43 times in 41 posts
Location: France
|
| Posted: Thu Jul 17, 2008 6:04 am Post subject: |
|
|
When you have this kind of equation, just factorize the left side by 2^x
You have to know that 2^(-x)=1/(2^x) and it's ok |
|
| Back to top |
|
|
anksanks
Just gettin' started!
Joined: 15 May 2008
Posts: 10
Thanks given: 0
Thanked 0 times in 0 posts
Location: India
|
| Posted: Thu Jul 17, 2008 6:44 am Post subject: |
|
|
2^x – 2^(x-2) = 3 * (2^13)
=> 2^x (1 – 1 / 2^2) = 3 * (2^13)
=> 2^x (3/4) = 3 * (2^13)
=> 2^x = 4 * (2^13) = 2^2 * (2^13) = 2^(13+2)=2^15
=> 2^x=2^15
=>x = 15
_________________
Shape me with your bounds,
Wrap me all around,
Define this adorable thought,
And break the silence.
(c) Anks |
|
| Back to top |
|
|
|
|
|
