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Is 4^x less than 5000?

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by thephoenix » Fri Jan 29, 2010 10:22 am
IMO B

s1)(4^x)*4>16000---->4^x>4000
insuff

s2)4*(4^x)=12288+4^x--->4^x=3072+(4^x/4)----->4^x(1-1/4)=3072---->4^x=3072*3/4=4096
yes <5000
suff

hence B
Last edited by thephoenix on Fri Jan 29, 2010 10:25 am, edited 1 time in total.
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by bhumika.k.shah » Fri Jan 29, 2010 10:23 am
If so, why so?
thephoenix wrote:IMO B
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by thephoenix » Fri Jan 29, 2010 10:26 am
bhumika.k.shah wrote:If so, why so?
thephoenix wrote:IMO B
edited
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by bhumika.k.shah » Fri Jan 29, 2010 10:33 am
hehhe

thanks!

Any other approach possible?
thephoenix wrote:
bhumika.k.shah wrote:If so, why so?
thephoenix wrote:IMO B
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by thephoenix » Fri Jan 29, 2010 10:39 am
bhumika.k.shah wrote:Is 4^x less than 5000?

A.4^x+1 > 16000
B.4^x+1=4^x+12288

Kindly explain step by step
another approach is damn easy
for yes no type of DS we need to c whether we get any ans

here s1) clearly 4^x is >4000 indicates a may be kind of situation so insuff

s2) one variable and one eqn hence one soln and it has to be either yes/true>5000 or no/false<5000
we need not to solve to find what the ans is
we just want to whether we can tell its true or false
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by bhumika.k.shah » Fri Jan 29, 2010 11:05 am
hmmm....well thats what i did for B and i knew B is for sure sufficient wasnt sure abt A and hence marked D :-(
thephoenix wrote:
bhumika.k.shah wrote:Is 4^x less than 5000?

A.4^x+1 > 16000
B.4^x+1=4^x+12288

Kindly explain step by step
another approach is damn easy
for yes no type of DS we need to c whether we get any ans

here s1) clearly 4^x is >4000 indicates a may be kind of situation so insuff

s2) one variable and one eqn hence one soln and it has to be either yes/true>5000 or no/false<5000
we need not to solve to find what the ans is
we just want to whether we can tell its true or false
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by ajith » Fri Jan 29, 2010 11:38 am
bhumika.k.shah wrote:Is 4^x less than 5000?

A.4^x+1 > 16000
B.4^x+1=4^x+12288

Kindly explain step by step
4^5 =1024

4^6 = 4096

4^7 = 16384


A implies x+1 is at least close to 7

x is at least close to 6 but not good enough to conclude whether 4^x is less than 5000

B. 4^7-4^6 = 16384 - 4096 = 12288
x=6

4^6<5000 sufficient
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