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perplexed

by naaga » Tue Mar 03, 2009 7:55 am
. If•represents one of the operations +, –, and ×,k . (r + m ) = ( k . r ) + ( k . m ) is for all numbers k, r and m?
(1) k•l is not equal to l•k for some numbers k.
(2) •represents subtraction.


I didn't understand the problem, anyone please explain this in detail
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Source: — Data Sufficiency |
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by quocbao » Tue Mar 03, 2009 8:33 am
Both choices lead to "." is subtraction, if you use substitution to check the answer.

So we have

k - ( r + m ) = k - r + k - m

or

k - r - m = 2k - r - m

It won't happen for all numbers => we can reply the question.

The answer will be D, I or II
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by scoobydooby » Tue Mar 03, 2009 1:14 pm
k . (r + m ) = ( k . r ) + ( k . m )?

stmnt 1: k•l is not equal to l•k for some numbers k
=> "•" is neither addition or multiplication. "•" has be subtraction.
k-(r+m)=k-r-m (LHS)
k-r+k-m=(RHS)
or k . (r + m ) not equal to ( k . r ) + ( k . m )
sufficient


stmnt 2: "•" represents subtraction
same info as in 1 above
sufficient
hence D
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by Ramp » Wed Mar 11, 2009 3:05 am
k-(r+m)=k-r-m (LHS)
k-r+k-m=(RHS)
or k . (r + m ) not equal to ( k . r ) + ( k . m )
sufficient

what if k is 0 .
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