Wikipedia:Reference desk/Archives/Mathematics/2010 December 10

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December 10

grade

Is my grade in the class correct? When I calculate my grade I get it should be 81 not 76. Is there something I am forgetting to do?grade Accdude92 (talk) 17:30, 10 December 2010 (UTC)

Yes, there is something you are forgetting to do. --COVIZAPIBETEFOKY (talk) 17:43, 10 December 2010 (UTC)

And that is?Accdude92 (talk) 17:45, 10 December 2010 (UTC)

All the numbers look correct to me. I'm not quite sure where you made a mistake, but it might be in not taking into account the weighted average of the total. Each sub category does not have equal weight in the final score. Instead, the scores in each subcategory are averaged together separately, and then the average scores for the subcategories are then used in a weighted average ( homework*0.20 + tests*0.5 + quizzes*0.3 ) to find the total score. -- 174.31.212.34 (talk) 17:48, 10 December 2010 (UTC)

(90)(.2)+(68)(.5)+(79)(.3) = 75.7, which agrees with your score.

A nonweighted average gives 79, so that can't be your only mistake. --24.27.16.22 (talk) 17:50, 10 December 2010 (UTC)

Here is what I did

(80+90+105+87+90+90)(.2)+(68)(.5)+(75+73+105+80+80+60+80)(.3)Accdude92 (talk) 17:54, 10 December 2010 (UTC)

That gives 308.3, not 81, and so cannot be what you did. Did you leave out some division in your work? --COVIZAPIBETEFOKY (talk) 17:59, 10 December 2010 (UTC)

Well what I really did was use my TI-84 plus calculator

I put 80 90 105 87 90 90 68 75 73 105 80 80 60 80 into L1 and .2 .2 .2 .2 .2 .2 .5 .3 .3 .3 .3 .3 .3 .3 into L2 went to 1 var stats L1,L2 and it says the mean is 81.13157895Accdude92 (talk) 18:06, 10 December 2010 (UTC)

Well, that explains it. The individual scores do not each have a weight of .2, .5, or .3. Their averages have those weights. If you really wanted to do it that way correctly, you would have to give each of the homeworks a weight of .2/6, the test a weight of .5, and the quizzes a weight of .3/7. --COVIZAPIBETEFOKY (talk) 18:10, 10 December 2010 (UTC)

Ohhhhhhhh lol ty so much!Accdude92 (talk) 18:12, 10 December 2010 (UTC)

As a fellow student I think there is something you are forgetting to do, and forgive me for being snarky but it is to do your assignments thoroughly and study for tests. Otherwise you would not have a C. 24.92.94.65 (talk) 01:20, 11 December 2010 (UTC)

Attempted Proof that P is not equal to NP (need peer review).

Can someone who's a higher authority in Math/Computing than I am point out the folly in my attempted proof that P!=NP? Please get in touch with me via my profile page or https://sites.google.com/site/pnproof/ .

Assume that sets P and NP are equal (P=NP), which means that we can prove that every problem (including the P versus NP problem) whose solution can be efficiently verified by a computer can also be efficiently solved by a computer. It follows that:

- We can determine sets P and NP, and prove that they're equal for every computable problem, both in polynomial time.

- Since we've assumed that sets P and NP are equal, let's first worry ourselves about how our algorithm will set about to prove that each polynomial time verifiable problem is also computable in polynomial time (set P).

- Assume it takes t1 (polynomial) time to discover the polynomial time (p1) solution to Problem1 (that belongs to set P, i.e. whose answer can be verified in polynomial time), t2 to determine that Problem2 (again, whose answer can be verified in polynomial time) can be solved in polynomial time (p2), and so on ... and tinfinity to prove that Probleminfinity can be solved in polynomial time (pinfinity).

- Now, to prove that the P_vs_NP problem itself can be solved in polynomial time, our algorithm has to perform two distinct tasks:

• Our algorithm has to first find the polynomial time solutions to each problem in the P class in polynomial time. Thus the running time for our algorithm to compute the set P (tp) for an infinite number of problems is:

tp= (t1 + p1) + (t2 + p2) + ... + (tinfinity + pinfinity)

For all problems in the NP class, it has to prove (in polynomial time) that no polynomial time solution exists.

tnp = nt1 + nt2 + ... + ntinfinity

where, nt1, nt2, .... nttinfinity are the polynomials representing the time to prove that problems NP1, NP2, ... NPinfinity belong to class NP.

Therefore the total running time to compute sets P and NP (assumed to be polynomial time for the sake of this proof) is:

tp_vs_np = tp + tnp

• Next, our algorithm has to prove (in polynomial time) that a polynomial time solution to compute tp_vs_np exists (i.e. that P_vs_NP belongs to class P). Let's call this pp_vs_np. In order to prove this however, our algorithm has to first discover a polynomial time solution to this infinite series (comprising the times to discover solutions to problems in infinite set P and the time to prove that every problem in set NP is infact non-polynomial). This is an infinite amount of time, since the P_vs_NP problem isn't solved until all of the infinite problems are correctly categorized as either belonging to class P or NP.

- Thus we reach a contradiction to our originally stated assumption that P=NP, which implied that the P_vs_NP problem itself, was solvable in polynomial time, which is not the case.

Thanks. Vivek (talk) 17:47, 10 December 2010 (UTC)

You thoroughly misunderstand what the classes P and NP actually mean. To begin with: you wrote

Assume that sets P and NP are equal (P=NP), which means that we can prove that every problem (including the P versus NP problem) whose solution can be efficiently verified by a computer can also be efficiently solved by a computer.

First, even if P = NP, it does not mean that we can prove it (especially since you are attempting to disprove it by a proof by contradiction). Second, "efficiently" is a vague notion used in several distinct meanings, make sure you read it as "polynomial-time". Third, and most importantly, the "P versus NP problem" itself is not an NP-problem. It is not even a problem in the sense used in the definition of NP, i.e., a set of finite strings over a finite alphabet. Everything from that point onwards is thus pure gobbledygook.—Emil J. 18:09, 10 December 2010 (UTC)

Thanks for taking time to explain it, I mostly get it now.Vivek (talk) 18:25, 10 December 2010 (UTC)