Arith Problem

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raunakrajan: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue Mar 16, 2010 8:27 am; Thanked: 1 times

by raunakrajan » Wed Jun 16, 2010 10:36 pm

if r*s = rs + s + r then for what value of s is r*s equal to r for all values of r?
(A) -1
(B) 0
(C) 1
(D) 1 / r+1
(E) r

Source: Beat The GMAT — Problem Solving | Wed Jun 16, 2010 10:36 pm

amising6: Master | Next Rank: 500 Posts; Posts: 294; Joined: Wed May 05, 2010 4:01 am; Location: india; Thanked: 57 times

by amising6 » Wed Jun 16, 2010 10:47 pm

if we take r as -1 we can wrte this equation as r*s=-1*s+s+r
r*s=r

Ideation without execution is delusion

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 am; Thanked: 135 times; Followed by:7 members

by selango » Wed Jun 16, 2010 11:24 pm

r*s = rs + s + r

r*s=s(r+1)+r

Plugin option and r will be -1

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