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46 replies to this topic

#41 mikedotcom



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Posted 03 June 2008 - 06:03 PM

I guess this depends on how you read the question. I read (1 brick is 1 kg) and (1 brick is half a brick heavy), not (1 brick is (1kg + half a brick) heavy). It's the difference between me reading "and" as a logical operator and you reading "and" as an arithmetic operator. Under my version, there are two options:

1. The term "brick" is ambiguous. You just said "one brick" weighs* 1 kg, so how can it also weigh 2 kg? If "one brick" is typical of "a brick" then the word problem is invalid:
1 brick = 1/2 brick
1 brick = 1 kg
1 kg = 1/2 * 1 kg
1 kg = 1/2 kg
1 = 1/2

Since 1 does not equal 1/2, 1 brick does not equal 1/2 brick and the problem is invalid.

2. If "one brick" is not typical of "a brick", then the problem changes:
1 [one brick] = 1/2 [a brick]
1 [one brick] = 1 kg
1 kg = 1/2 [a brick]
2 kg = [a brick]

1 [one brick] = 1/2 [a brick]
1 kg = 1/2 * 2 kg
1 kg = 1 kg
1 = 1

Since 1 does equal 1, this version is accurate, "one brick" weighs 1 kg and "a brick" weighs 2 kg. However, the question is not how much "a brick" weighs, but how much "one brick" weighs, so no math is necessary: "one brick" weighs 1 kg, as stated, and the answer is 1 kg, not 2 kg. As I read it, it's a very simple logic problem designed to confuse by seeming more complicated than it is.

Under the other interpretation, your answer of 2 kg is valid, but it's not a logic problem anymore.

* Technically, kg measures mass, not weight. So a valid answer on Earth would either be 2.2 lbs (the weight of 1 kg sitting on the surface of Earth) or 4.4 lbs (2 kg), depending on which interpretation we went with. Since you said "how heavy", not "what is the weight", this may be an inaccurate semantic argument, but is something I came up with under the logic realm.

you really missed this one, I think you over-thought it LOL
your premise to begin is invalid: 1 brick = 1/2 brick
the problem stated" 1 brick = 1 kg + 1/2 brick
be careful on your assumptions and keep on trying!
otherwise your technical analysis is very well thought out
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#42 PlumeDeNom



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Posted 29 June 2008 - 11:36 PM

1 brick = 1kg + 1/2 brick

how heavy is 1/2 a brick?
1/2 brick = 1/2kg + 1/4 brick

how heavy is 1/4 brick?
1/4 brick = 1/4kg + 1/8 brick

etc. etc. etc...

so basically it becomes: 1 Brick = 1 + 1/2 + 1/4 + 1/8 + 1/16 + 1/32 +...+ and so on

even though when u solve for the equation you get: (brick = x)
x = 1 + 1/2x
x - 1/2x = 1
x(1-1/2) = 1
x = 1 / (1 - 1/2)
x = 2

the real weight of 1 brick never really reaches 2. Instead, its
1.99999 > 2
(you can add as many 9s as u want...)

Well it actually does as that 1.99999.... = 2

check it out:

let x=1.9repeated.

then 10x = 19.9repeated
subtract x = 1.9 from that and you get:
9x = 18
divide both by 9

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#43 Charlie87


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Posted 09 November 2008 - 08:31 AM

Wow, i cant believe there's so many responses to such an easy problem...

Ok ppl, I think the easiest way to go about solving this problem without any algebra or whatever else, is to simply use ur imagination. Sounds cheesy, but picture this:

Picture a balance, on one side is one brick and on the other side is half a brick PLUS a KG of whatever the heck u'd like to imagine.... (rocks in a bag, eggs, whatever)

Now, since the two sides must obviously balance out, since the problem stated this, you must know that the half-brick has to equal the kilo of whatever you have to balance with the other whole brick. Because its like having 2 halves of brick on one side and on the other the half brick plus something that weighs the SAME as half a brick (which is the 1kg). So the solution becomes very obvious once you picture that.

I do have to admit, it was a bit confusing at first with the way it was worded, but a little bit of thinking and.... it was a piece of cake B))
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#44 KMM



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Posted 01 December 2008 - 05:52 AM

1 brick equals 1 and 1 and a half kgs is the the answer because one brick =one kg and half a brick so half of a brick would be half a kg. right?
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#45 Xerolooper



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Posted 19 March 2009 - 04:31 PM

Problems like this always frustrated me in school because Like many people posting answers here I am too smart. What I mean is this riddle is valid but stated but in an ambiguous manner. You would never state the question like the original poster did because you recognize it as ambiguous. If you assume that the person asking the riddle is also smart enough to recognize that its ambiguous you then assume there must be something your missing. What the riddle should teach you is not some new mathematical equation but rather to look at problems differently. Often in life you are dealing with people who will not recognize their own ambiguity. So try to relax and realize that the simplest answer is usually the right one. Although I admit my very first thought was 1 brick = 1 kilogram but then I reread it and realized 1 brick = 1 kilogram and(+) 1/2 a brick that is natural and I believe the intent of the riddle.
Spoiler for Simple is as simple does.

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#46 Pet_Rock


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Posted 19 March 2009 - 07:04 PM

Brick - Back to the Logic Puzzles
One brick is one kilogram and half a brick heavy.
What is the weight of one brick?

Spoiler for Solution

Spoiler for old wording

I guess its a matter of perseption:
Spoiler for My view is

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#47 Prof. Templeton

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Posted 19 March 2009 - 08:27 PM

I guess its a matter of perseption:

Spoiler for My view is

I think the weight is uniform for all bricks, so there is only 1 unknown (the weight of the brick), not 2
Spoiler for equation

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