Posted 07 May 2007 - 06:55 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.