Question

7. Arrival of the Normandy Train

Claude is waiting to meet the train from Normandy at Gare Saint-Lazare in Paris. He
tells Marie the hour of the train's arrival and he tells Jean at which minute it arrives. He
also tells them both that the train arrives between 0600 and 1000.
They consult the timetable and find the following services between those times:
0620, 0639, 0650; 0717, 0746; 0825, 0839; 0917, 0925, 0950.
Marie then says, “I don't know when Claude's train arrives, but I'm sure that neither does
Jean."
Jean replies, “I didn't know his train, but now I do."
Marie responds, “Now I do as well!"
When is Claude's train and how do you know?

Answer 1

0839

Explanation:

First of all, let's cancel 0620 and 0746, because they dont have any other number that has the same last 2 digits as them. Jean would've immediately known the train number if it was one of these two.

Now, when Marie says "I'm sure that neither does Jean", it means she is guaranteed Jean doesn't know the train number. It mean she couldnt've gotten 06 or 07, as 0620 and 0746 have it.

We're left with 0825,0839,0917,0925 and 0950
When Jean replies he knows the train number, it means he couldnt've gotten 25, as it's repeated.

And when Marie responds she knows as well, she couldnt've gotten 09, as it's also repeated.

We can cancel 0825,0917,0925 and 0950

So, the train number is 0839