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#1 2008-01-21 07:21:12

tony123
Member
Registered: 2007-08-03
Posts: 189

3/5

If

then

(a) x<y        ( B)  x> y        (C)x=y          (D)noon of these

Last edited by tony123 (2008-01-21 07:21:59)

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#2 2008-01-21 08:04:56

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: 3/5

(a) can be true; for example x can be 3 and y can be 5
(b) can also be true (but then (a) obviously wouldn't); for example, x can be -3 and y can be -5
(c) cannot be true
(d) cannot be true, as (a) or (b) can be true

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#3 2008-01-21 08:23:36

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: 3/5

I interpret (D) as "It is impossible to say that any previous statement is true", as opposed to "The previous statements are not true".

If it was the second case then you could immediately tell it was false without reading the question, because one of x<y, x=y and x>y will always be true, regardless of what x and y are.

The correct answer is (D) by that interpretation, because as Daniel has shown, it's possible for (A) or (B) to be true (and so we don't know which is).


Why did the vector cross the road?
It wanted to be normal.

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#4 2008-01-21 10:18:30

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,535

Re: 3/5

Yes, I would also say (D) because you cannot rely on (A) being true, neither can you rely on (B).


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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#5 2008-01-21 10:43:11

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: 3/5

mathsyperson wrote:

I interpret (D) as "It is impossible to say that any previous statement is true", as opposed to "The previous statements are not true".

I would (now) also say (D). smile

Last edited by Daniel123 (2008-01-21 10:43:26)

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#6 2008-01-23 01:51:10

ganesh
Moderator
Registered: 2005-06-28
Posts: 14,522

Re: 3/5

I too agree. (d) is the best option.
It has not been said whether a and b belong to set of natural numbers, integers or rational numbers.


Character is who you are when no one is looking.

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#7 2008-01-23 05:06:54

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: 3/5

Fair point, if we're dealing with naturals then the answer would be (A).
Tony's puzzles tend to work with reals though.


Why did the vector cross the road?
It wanted to be normal.

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