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k^2 - k

by harsh.champ » Wed Feb 17, 2010 5:46 am
What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
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by shashank.ism » Wed Feb 17, 2010 7:19 am
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
(k^2 - k)--> K(K-1)
st.1 (k - 1/k) is 1. --> k-1 =k --> not possible --- insufficient
st.2 d/dk (k^2 - k) = 2k-1= sqrt 5 --> (k^2 - k) = k(sqrt 5) +c --insufficient

combined insufficient Ans E
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by Osirus@VeritasPrep » Wed Feb 17, 2010 7:21 am
shashank.ism wrote:
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
(k^2 - k)--> K(K-1)
st.1 (k - 1/k) is 1. --> k-1 =k --> not possible --- insufficient
st.2 d/dk (k^2 - k) = 2k-1= sqrt 5 --> (k^2 - k) = k(sqrt 5) +c --insufficient

combined insufficient Ans E
You didn't show why you don't get any new info when they are combined, could you explain that?
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by shashank.ism » Wed Feb 17, 2010 7:30 am
osirus0830 wrote:
shashank.ism wrote:
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
(k^2 - k)--> K(K-1)
st.1 (k - 1/k) is 1. --> k-1 =k --> not possible --- insufficient
st.2 d/dk (k^2 - k) = 2k-1= sqrt 5 --> (k^2 - k) = k(sqrt 5) +c --insufficient

combined insufficient Ans E
You didn't show why you don't get any new info when they are combined, could you explain that?
since we don't get any value from st. 1 so st1. and st2. combined will not give any value. so we go for ans E.

If in case we consider something from st.1 i.e. there is no possible value of k from statement 1 then k^2-k also has no possible value ..so in that case Ans A


so there is a bit confusion ..Rather I would go for E
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by cunazza » Wed Feb 17, 2010 7:30 am
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
(1) (k-1) /k = 1 => k-1 = k => 0=1 => not possible => INSUFF.
(2) 2k-1 = sqrt5 => k = (sqrt5 + 1)/2 => substitute this value into the original (k^2 - k) => SUFF.
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by shashank.ism » Wed Feb 17, 2010 7:43 am
cunazza wrote:
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
(1) (k-1) /k = 1 => k-1 = k => 0=1 => not possible => INSUFF.
(2) 2k-1 = sqrt5 => k = (sqrt5 + 1)/2 => substitute this value into the original (k^2 - k) => SUFF.
ok u r right ... The ans will be B. I actually saw integration of 2k-1 as K^2 -k and got confused ...k = (sqrt5 + 1)/2is sufficient to solve out the value of (k^2 - k)

thanks..
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by money9111 » Wed Feb 17, 2010 7:53 am
yeah i'm going to go with cunazza on this one because since 2 is an equation with 1 variable we dont even need to solve because we know that it is solvable! and since 1 is just insufficient which i think we all agree on... B is the answer
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by ajith » Wed Feb 17, 2010 9:14 am
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
The question is poorly made, one choice doesnt even make sense, may I ask the source? I know this is a query that will not be answered.
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by shashank.ism » Wed Feb 17, 2010 9:17 am
ajith wrote:
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
The question is poorly made, one choice doesnt even make sense, may I ask the source? I know this is a query that will not be answered.
yeah I think question really confuse us ..As st 1 gives no solution which also makes a sense that there will b no value for (k^2 - k).. so it may be considered sufficient or insufficient

I am confused whether I should go with B or D....
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by kaustubh_b » Wed Feb 17, 2010 9:51 am
I see here that statement 1 is: (k-1/k) and not (k-1)/k.
This means, (k^2-1)/k = 1
=> k^2 - 1 = k
=> k^2 -k = 1 -> SUFF

From Stmt 2,
2k-1 = sqrt(5)
=> (2k-1)^2 = 5
=> 4k^2 - 4k + 1 = 5
=> 4k^2 - 4K = 4
=> k^2 - K = 1 -> SUFF

Hence, answer is D
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by shashank.ism » Wed Feb 17, 2010 9:54 am
kaustubh_b wrote:I see here that statement 1 is: (k-1/k) and not (k-1)/k.
This means, (k^2-1)/k = 1
=> k^2 - 1 = k
=> k^2 -k = 1 -> SUFF

From Stmt 2,
2k-1 = sqrt(5)
=> (2k-1)^2 = 5
=> 4k^2 - 4k + 1 = 5
=> 4k^2 - 4K = 4
=> k^2 - K = 1 -> SUFF

Hence, answer is D
Yeah kastubh thats cool lastly you have given a right solution ..thanks .. I really got confused between (k-1/k) & (k-1)/k.
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by harsh.champ » Wed Feb 17, 2010 11:03 pm
ajith wrote:
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of [(k) - (1/k)] is 1.
(2) The value of 2k -1 is sqrt 5 .
The question is poorly made, one choice doesnt even make sense, may I ask the source? I know this is a query that will not be answered.
Well ajith,
Surely your query will be answered.It is taken from my sheet of D.P.S.(Daily Practice Sheet) which we get over here.As for the question ,what is confusing?I think the change made by me above makes it clear now.Were you confused that it was (k-1)/k or was it some other query?
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by harsh.champ » Wed Feb 17, 2010 11:07 pm
harsh.champ wrote:What is the value of (k^2 - k)?
(1) The value of (k - 1/k) is 1.
(2) The value of 2k -1 is sqrt 5 .
Guys,I will post the soln. now.If still you have another query,just let me know.

Soln:-
(1):-We get (k^2 - 1)/k = 1
=>k^2 - k - 1 = 0
=>k = [1 + sqrt(5)]/2
Hence,sufficient.

(2):-We get 2k - 1 =sqrt(5)
=>2k = 1 + sqrt(5)
=>k = [1 + sqrt(5)]/2
Hence,sufficient.

So,the answer will be D.
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