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Grockit- PS-must be true

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Grockit- PS-must be true

by arora007 » Mon Dec 13, 2010 6:45 am
If a and b are different positive integers and a + b = a(a + b), then which of the following must be true?


I. a = 1

II. b = 1

III. a < b

A) I only
B) II only
C) III only
D) I and II
E) I and III

I liked this one, If u dont rush you will get it right
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by frank1 » Mon Dec 13, 2010 7:58 am
I think it should be E
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by N:Dure » Mon Dec 13, 2010 8:22 am
E

If a= 1 and b then has to be different so = 2 a+b = 3 = a(a+b) = 3

if b=1 and a=2 a+b=3 a(a+b)= 6

Then a =1 works and b has to be different so it must be bigger ie. a<b
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by mj78ind » Mon Dec 13, 2010 9:34 am
arora007 wrote:If a and b are different positive integers and a + b = a(a + b), then which of the following must be true?


I. a = 1

II. b = 1

III. a < b

A) I only
B) II only
C) III only
D) I and II
E) I and III

I liked this one, If u dont rush you will get it right
Ok am a bit rusty :)

(a+b) = a((a+b)

=> (a-1)(a+b)=0

This is only possible if a= 1. Now a and b are different if a= 1, then b has to be greater than 1 since both are different positive integers. Hence E
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by arora007 » Mon Dec 13, 2010 10:00 pm
yeah..its E... hope nobody chose A like I did when I had about 30 seconds for the problem!
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