Incorrect answer in the 'cube' task

I'm not a math user but I have downloaded gbrainy source and check that algorithm for obtain right answer fot this problem is resolved by:

rows = columns = deepth = 4 + random.Next (max_random);
ans = rows * columns * deepth;
right_answer += ans.ToString ();

For example if your case you have a cube with 4 rows, 4 colums and a deepth of 6 (faces of a regular cube), so in resume we have:
ans = (4 * 4 ) * 6 = 96

@Kamus: Ok, I'll check it out this weekend when I get 5 minutes.. Thanks for the comment :).

@Kamus, what?

If rows = columns = deepth = 4, then ans becomes 4*4*4 = 64. But that's not the correct answer, neither is 96. The correct answer is 99.

'Deepth'" (should be 'depth' of course) is not the number of faces. It's the number of cubes in the third dimension.

The correct code should be

n = random.Next(max_random)
ans = 0
for i in xrange(2, n + 1):
  ans += i**3

Alternatively, one can use the closed-form formula to compute the sum:
n = random.Next(max_random)
ans = (n*(n + 1) / 2)**2 - 1

It should be noted that in the case of unequal dimensions (i. e. rows, cols and depth differ from each other) the task gets a bit harder.

Hello folks,

Thanks for the feedback. I think that the problem is that the question clear enough for everybody bringing this confusion.

I would like to keep the puzzle simple. The user basically should count the 1x1 cubes.

Instead of the current question:

"How many cubes do you count in the figure below? (not counting the figure) Answer using a number"

I would suggest:

"How many single small cubes do you count in the figure below? Answer using a number"

What do you think?

Regards,

Jordi,

Note: See a very similar game[1]

[1] http://www.interactivestuff.org/sums4fun/3dboxes.html

@Jordi Mas, yes, that will be OK but not too interesting to solve. I think almost everyone can easily guess, that he should just raise the number to the power 3. The game you noted is better, because it features boxes and not only cubes, thus taking some time to perceive an image.

gbrainy allows the possibility to show different versions of the puzzle depending on which difficulty level you are playing.

I suggest two actions here:

1. Short term (for the 1.4x) maintenance series, fix the current wording of the question to make it work as it is now (easy / medium difficulty level).

2. Medium term (for gbrainy 1.5x release) include a more complex puzzle for master difficulty level.

Can you please guys confirm that the changes in the wording of proposed in comment #5 will clarify the current puzzle as it is? (easy)

Can you give please provide a version (just the question, and answer, and rationale, I can do the coding) of the same puzzle that is more complex for inclusion on gbrainy 1.5?

Thanks a lot for your help

Jordi,

Yes, I think that wording change from comment #5 will do. But is it an easy fix? Don't forget about i18n. If we consider a short-term maintenance series, maybe it's easier to fix the answer as suggested by me in the comment #4.

Some thoughts about 1.5x version:
1) Easy level:
"How many single small cubes do you count in the figure below? Answer using a number"
The figure is always a cube.
2) Medium level:
Same question, but the figure is any box.
3) Hard level:
"How many cubes do you count in the figure below? (not counting the figure)"
The figure is a cube.

I actually got this one wrong. Or rather, I think the n^3 answer is wrong.

The question says "the figure" below, and while it immediately looks like a cube, there is no way to know whether the figure is hollow. Thus, the only correct answer would have to be the sum of small cubes visible from the three sides visible to the user.

Thus for the 6 x 6 x 6 figure, the answer would be 6x6 + 5x6 + 5x5.

Thus, the question should point out that the figure is a complete cube in order for the n^3 answer to be correct.

Hello,

Some more precision will do no harm. Instead of saying:

"How many single small cubes do you count in the figure below? Answer using a number."

I propose to say:

"How many single small cubes do you count in the large cube below? Answer using a number."

Let me know what you think.

Regards,

Jordi,

How about "How many small cubes does it take to build the large cube below?" - this implies that you need to count the physical cubes not the logical ones.

Agreed. I commit it the fix. Thanks. Jordi,

That would be better :)