Heads or Tails challange - Answer at end

TopographicOceans

Have someone lay out a hundred coins on table with 90 of them with the obverse facing up.

Without looking at them and with your eyes closed, can you separate all the coins into two groups so each group has the same number of reverses facing up?

messydesk

As long as it isn't someone's lowball set.

LindeDad

Nope only do the slabbed stuff.

lkeigwin

Are they all the same coin type?

Lance.

EagleEye

Your challenge means that there are 5 coins in each group with reverses showing. Odds are good that you'll get close to that just by random luck. It would be a certainty that you would be +- 5 from the correct outcome.

TopographicOceans

Take any 10 coins and set them aside and turn them over. This becomes group #1.

The rest of the coins become group #2.

Open your eyes and you will see both groups have the same number of reverses facing up.





Why it works:
10% of the coins have the reverses up. If you move 10% into a group and turn them over, then 10% will be up in both groups.

ambro51

You guys have too much free time

mustangmanbob

Originally posted by: TopographicOceans
Open your eyes and you will see both groups have the same number of reverses facing up.

Each group does not have the same number of ob / re showing, only if the groups are treated as a singularity.

david3142

TO, the process is right but the explanation is wrong. If there are n heads and 100-n tails, take a group of n coins. Let q denote the number of heads in this group. So we have q heads and n-q tails. Now flip them all. We have q tails and n-q heads. In the other group we also have n-q heads (since we started with n and removed q).

roadrunner

Interesting.

IrishMikey

Originally posted by: david3142
TO, the process is right but the explanation is wrong. If there are n heads and 100-n tails, take a group of n coins. Let q denote the number of heads in this group. So we have q heads and n-q tails. Now flip them all. We have q tails and n-q heads. In the other group we also have n-q heads (since we started with n and removed q).

Are you allowed to talk like that in a public forum?

coindeuce

Originally posted by: david3142

TO, the process is right but the explanation is wrong. If there are n heads and 100-n tails, take a group of n coins. Let q denote the number of heads in this group. So we have q heads and n-q tails. Now flip them all. We have q tails and n-q heads. In the other group we also have n-q heads (since we started with n and removed q).

Doctorate in statistics, or math ?

david3142

I have an undergrad degree in physics but didn't want to pursue a PhD.

TwoSides2aCoin

My nephew asked me : "Did you ever notice geese fly in a V formation ? " I say "Yeah, almost always". He asks : " Did you ever see that one side of the V is longer than the other, typically ? ". I thought for a second and said, "Yeah, I've noticed this ". He asked me " Do you know why ? "


The answer surprised even me.