Random puzzle v4

The probability that he gets exactly one incorrect?

IT IS ZERO he can't get just one incorrect. If one wrong check is in an envelope then the other envelope has a wrong check too. 

Happy7's dumbness is contagious!

I believe that would be 1/16.  I just woke up, so don't blame me if I'm wrong.

Sorry that's wrong. Think about it more carefully.

1/30?  My brain just isn't working.  I need to eat

4*1/4*2/3*1/2*1=1/3  Maybe 

I said the prob that the first one is right is 1/4

The prob that the 2nd is wrong is 2/3

The prob that the 3rd is wrong is 1/2

The prob  that the last one is wrong is 1

BUT

it could be the 1st or 2nd or 3rd or 4th that is right so i multiplied by 4

I won't guarantee that it is correct but it sounds ok to me. :)

There are 24 possiible arrangements.......

Let's look at the possible arrangements with  cheque 1 going into envelope 1.

So we have

1 2 3 4

1 2 4 3

1 3 2 4

1 3 4 2

1 4 2 3

1 4 3 2

Note that only 2 of these have cheque 1 going into  envelope 1 and all the others the wrong ones. These would be 1 3 4 2  and 1 4 2 3. So, that is 1/3 of the possible arrangements where  cheque 1 goes into envelope 1.

And every other arrangement (2nd check in 2nd envelope, etc.) would have the sme probabilty.

So, the answer - I think - is 1/3.......

Yes nauseated is correct.   If one is wrong another one has to be wrong.

There you go Happy, you are in good company - we are all  'stupid'  

OH except for nauseated of course - he is just nauseating.    LOL