Brain Teasers

1. After a local Post Office burglary, five suspects were being interviewed. Below is a summary of their statements.
Police know that each of them told the truth in one of the statements and lied in the other. From this information can you tell who committed the crime?

Brian said:
       It wasn't Charles;
       It was Alan

Derek said:
       It was Charles;
       It wasn't Alan

Charles said:
       It was Brian;
       It wasn't Eric

Alan said:
       It was Eric;
       It wasn't Brian

Eric said:
       It was Derek;
       It was Alan 

Ans: Remember that each person told exactly one truth and exactly one lie. So Derek was the culprit. How can you reason this out?
Looking at Brian's statement if it was Charles, then Brian was lying in his first statement, which makes the second statement true. Which would mean that it was both Charles and Alan. So it can't be Charles.
Which means Derek was lying in his first statement, which makes the second statement true. Therefore it can't be Alan.
So Eric's second statement must be false, meaning his first statement was true, therefore it was Derek.

2. You have the misfortune to own an unreliable clock.

This one gains exactly 15 minutes every hour.

It is now showing 3.00am and you know that is was correct at midnight, when you set it.

If the clock stopped four hours ago, what is the correct time now?

Ans:  It is 6:24 AM. To figure out this, the first thing is to find out how many clock-minutes pass for each real hour.
Since the clock is gaining 15 minutes every hour, for every real hour that has passed, the clock will show 75 minutes.
Since the clock shows 3.00 AM, we know that 180 clock minutes have passed. This equals 144 real minutes (180 / 75 x 60), so the clock shows 2.24 AM.
The clock stopped 240 minutes ago (4 hours), so the time must now be 6.24 AM.

From: brainbashers.com