"Fun" Math problems thread! (Yay)

We have a winner! Wooo!
Your work leaves a bit to be desired, and I used a different condition (ax=0 instead of ay=g, so everything I had was worked out in x, not y!), but your answer for the magnitude of N is correct, so I trust that you got the right answer. (2) follows from (3) in any case, so I’ll give it to you :wink:

But you were so close! And it’s not so bad, just a couple of bits you need to tack onto N.

I’ll have that promised shiny golden physics star to you as soon as finals finish up. :grinning:

Now generalize for y=kxn

What do you mean? We’re all enrolled at the university of Huck. We have our own programing class lead by @NavyFish and co. We have a screenshot class by @Hutchings and now we have a suffering class by these folks here.

Edit: On that note, I wish I had time to actually search for materials to be able to do this type of math solving/proofing. But I’ll have to stick to simple carpenters math (Which oddly enough is the most confusing shit in the world sometimes.)

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If you think that’s bad, you should see my scratch pad! 4 pages of doing #2 wrong. 1 page of doing it right!

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If people would like more, I’m full of problems like these. Feedback first, though. Are they too tough? Too easy? Any preferences for subject material? As y’all might have guessed, I was pretty infatuated with classical mechanics, but I can be flexible. Probability problems are another favorite of mine, and I can probably dig up some neat abstract algebra problems or something. :wink:

I can also provide a worked solution to the quadratic slope problem if people desire… Tomorrow. Finals studying tonight.

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Guys, I need a little help in Probability. I have this problem: From a deck of cards (52) we remove the face cards (J, Q, K) with probability 1/2 (each one). After that we draw 5 cards from the remaining ones. If X is the number of aces in the hand then calculate E[X]. Thanks for anyone who can solve it :smile:

(I tried to solve it assuming that X is a hypergeometric variable conditioned by Y, a binomial variable with parameters n=12 (all the face cards) and p = 1/2. Then i calculate E[X] = Sum(E[X|Y=y]P(Y=y)) where E[X|Y=y]= 5*4/(52-y), the expected value of the hypergeometric variable and P(Y=y) is the
density of Y in y. Well that formula is pretty ugly, i calculated it and the value was near 10/23, one of the possible answers to the question in my exam simulation, but not equal to… so i think there must be another way to do this!)

Just got out of an analysis test. This cute problem grabbed my attention:

A function f is differentiable on an interval (a, b).
The function g = f*f’ = 0 on (a, b).

Show that f must be a constant function.

My solution was a single line, so don’t overthink it! :wink:

Given two values, p and q, such that pq = 0, either p, q, or both p and q must be zero. This applies to functions as well.

That means, on the interval (a,b), either f(x) = 0, or df/dx = 0, or both. And since f(x) = 0 is a constant function, and df/dx = 0 requires a constant function, all roads lead to f(x) = const.

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I’ll accept this!

My answer was different in form, so I’ll include it too.

d/dx(f^2) = 2f*f’ = 0 by given info. This implies f^2 is constant which implies f is constant.

Math comes back with a vengeance. Just kidding, but I stumbled upon this little “problem” on a news site (the articles headline was something along the lines of ‘The net goes crazy over trying to find all the triangles. Can you find them all?’, so I didn’t bother actually reading it, just took a look at the picture which showed the triangle). I wasn’t interested in drawing in every triangle possible, but I wanted to know, how many triangles there are so I did some calculations and thought it would be fun to share this with you. So, what do you think?

How many triangles are there? (and more importantly: how did you reach your conclusion?)

(really) Quick reply before food time,

Either 5 or 7, depending if you count whether or not something ‘counts’ as a triangle if it has other shapes inside.

Let’s assume that any shape that is constructed using 3 straight lines that intersect with each other counts as a triangle, no matter what other (if any at all) shape(s) is/are inside of that shape.

Ah, see now.

…

Ah, also to be clear, those intersections of the 3 lines must not share the same coordinates.

I count 10. The base triangle, then the 2 put together to make the base. Then 2 more making the top left of those 2(the equilateral). Then the top 3 double inner, 1 in the middle, 1 on the bottom left. That makes 10.

My triangles are defined as triangles…where the sum of the angles is 180 degrees and have 3 sides.

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I’m currently 16 and counting. There’s probably a formula to make this easier … :stuck_out_tongue:

Actually I’m stuck at 16.

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Ooh 6 extra. Wish I could see those. I believe there is, this reminds me of graph theory in discrete. Theres definitely a formula where you count the edges and vertices and get some sort of answer.

Edit: I see em now. Up to 20.

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I’m hungry… why am I counting triangles and not eating… :frowning:

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I’ve got coffee at least…that’s like food!

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My glass of water on my desk has a few drops left… it’ll have to do. :wink:

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Joules are Joules!

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