Hearted Youtube comments on Mathologer (@Mathologer) channel.
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Challenges:
1) We can guarantee at least 5 on one side. There are two ways to split the pigeons: 3-2 and 4-1. The max you can hit for both of them is 3 and 4 respectively. So we have at least 3 pigeons on one side. Add in the two pigeons on the equator and we have 5.
2) let the mystery value equal x. by multiplying by 10^some integer until the digits line up again, and then subtracting, we have 10^whatever*x - x = the non-repeating part you're left with. Factor out x on the left and that 10^whatever - 1 becomes a bumch of 9s. Then divide and we have the non-repeating remainder over a bunch of 9s. If ever the remainder isn't an integer just multiply both the numerator and denominator by 10 to knock out the decimal.
Example: 0.4318181818...
x = 0.4318181818...
100x = 43.18181818....
99x = 42.75 (all the 18s afterward cancel out)
x = 42.75/99
x = 4275/9900
x = 19/44 (simplify)
3) let's pretend we color the "didn't shake hands" white. We leave the "shook hands" black. So all we have to do is prove a triangle exists somewhere, and it doesn't matter what color. Note that each dot will always have at least three lines of the same color connecting to it, for the same reason the pigeons in challenge 1 can be split into a side with at least 3 and a side with less.
Look at a point, and follow three lines of the same color (I'll choose black) to three other points. Any line connecting two of these three points would either be black or white. If it were black, that would make a triangle with the two points and the starting point. If it weren't, then the three dots all have white lines between them, which makes another different triangle.
4) 315. And no, I didn't count manually. Here's how I found out:
The 7 edges UB, UR, RB, DB, DL, LB, and UL, all commute in one big cycle of length 7. The remaining 5 edges do the same. The 5 corners URF, ULF, DRF, DLF, and DRB go back in their positions but in the wrong orientation. So it takes 3 cycles to get back to their original orientation. The same thing happens with the other 3 corners in the back, only this time they take 9 cycles because they permute around each other too as well as reorient themselves.
All that's left is to compute the lcm of 7, 5, 3, and 9, which turns out to be 315.
5) 1, 2, 4, 8, 16, 32, and 64. Any collection just results in the binary representation of the number. Since every number can be written in binary in only one way, every single collection will add to a different number.
6) Queen of Hearts. The 9 of Hearts at the start signals the suit of the missing card is Hearts. The remaining three kings can be sorted as MBT (Diamond, Club, Spade), which is assigned 3. 3 spots after 9 is the Queen, and putting it all together we have Queen of Hearts.
Edit: I forgot one, challenge 5 at chapter 6
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6:28 - The reason taxes come out first isn't some kind of greed on the part of government. It's because only paying the taxes first ensures that nobody will go bankrupt to their friends as a means of avoiding the payment of taxes to the government. If my assets are only just enough to cover my back taxes, I can call my friend and say "Do you remember that money I borrowed from you 20 years ago? We kinda forgot about it, but I think it's time to formalize it with a document because I'm about to go bankrupt". The friend comes over and I sign the note, which is for 99 times the amount of my assets. If taxes are not given priority, then when I go bankrupt the government gets its penny on the dollar in proportion to all debts, while my friend gets 99 cents on the dollar. When the dust settles, my friend simply gives me back that 99% of my assets. I end up losing 1% to back taxes instead of 100%. But if everyone knows that taxes come first, then everyone sees the fruitlessness of such schemes and they won't be attempted. Of course, I can run this same scheme on any NON-governmental entity to whom my debt equals my assets, and get 99% of everything back while the debt to that creditor is marked "paid in full". That creditor will go to court and challenge the validity of a promissory note signed one day before a bankruptcy-filing, but the government, by taking taxes first, doesn't have to go through that hassle.
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