Pure maths, physics, logic (braingames.ru): non-trade-related brain games - page 50

 
MetaDriver:

Is it really 1/2 ???

))))))))

I was referring to your answers to the two sub-paragraphs.
 
alexeymosc:
Nat. OK first answer = 1/3 and it's correct.
I'll keep pushing! The second answer is also correct.
 
MetaDriver:
I'll keep pushing! The second answer is also correct.

And why is that? I have a different answer, I can give you a reasoning.

You have it that with every flip, the coin is taken out of the pocket anew! And it is pulled out once and flipped after that.

PS: you get the probability of pulling out a fair coin (with the flip giving tails) 10 times in a row.

 
alexeymosc:

And why is that? I have a different answer, I can give you a reasoning.

You have it that with every flip, the coin is taken out of the pocket anew! And it's taken out once and tossed after that.

That's exactly the opposite. If it was pulled out every time, then after every flip, the probability would be 1/3

And if you draw once and ten times it comes out that points to a fair coin with probability 1/3 ,

then the probability after the tenth throw = 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 * 1/3 = 1/3^10 = 1/59049

 
alexeymosc:
Nope, conditional probabilities here.

.....The first one has two coins in his pocket. .... Megamind randomly pulls a coin out of his pocket ....

tosses / doesn'ttoss the odds don't change = 1/2

and 1,000 timeshe can flip...probability doesn't change....

If he flipsa coin 1000 timesand gets 1000 tails, what will be the probability on 1001 times he gets tails again?

My guess is 1/2 ....

:)))

 
MetaDriver:

It's exactly the opposite. If it were pulled out every time, then after any shot, the probability would be 1/3


It wouldn't be 1/3 after any shot, it's only after tails. Not the point...

What is the probability of throwing 10 tails on a fair coin? 1(/2^10). And on a coin with two tails it is 1. And what is the probability of picking a fair coin from your pocket - 0.5.

Further it is simple. What is the probability that the coin is fair if 10 tails are struck? All probabilities are given here.

 
Manov:

.....The first one has two coins in his pocket. .... Megamind randomly pulls a coin out of his pocket ....

tosses / doesn'ttoss the odds don't change = 1/2

and 1,000 timeshe can flip...probability doesn't change....

If he flipsa coin 1000 timesand gets 1000 tails, what will be the probability on 1001 times he gets tails again?

My guess is 1/2 ....

:)))

Solution prompt: we have 3 elementary events:

1. a fair coin is pulled out and 10 tails are tossed;

2. pulled a fair coin and did not get 10 tails out of 10 tosses;

3. pulled a foul coin and got 10 tails (no other option).

 
alexeymosc:

After any throw, it would no longer be 1/3, it's only after tails that way. Not the point...

What is the probability of tossing 10 tails on a fair coin? 1(/2^10). And on a coin with two tails it is 1. And what is the probability of picking a fair coin from the pocket - 0.5.

Further it is simple. What is the probability that the coin is fair if 10 tails are struck? All the probabilities are given here.

Nah. Illogical.

The result of the first one (pulling a fair/dishonest coin) must be calculated from the ten flip results.

After each flip with the result "tails", the probability that the coin is fair falls by a factor of three.

The first version is correct.
 
MetaDriver:

((((((5115+1)*5/4+1)*5/4+1)*5/4+1)*5/4+1)*5/4+1) = 15621

Nothing less...

All solutions are written with the formula 1+5*(4+5*(4+5*(4+5*(4+5n))))), with n=0 we get 15621
 
MetaDriver:

Nah. illogical.

The result of the first one (pulling a fair/dishonest coin) must be calculated from the ten flip results.

After each flip with a "tails" result, the probability that the coin is fair drops by a factor of three.

The first version is correct.
My answer to the second part of the problem: 1/1025. If you don't believe me at all, let's wait for at least one more reasonable solution and compare ;)
Reason: