logical questions

1. Three men in a cafe order a meal the total cost of which is $15. They each contribute $5. The waiter takes the money to the chef who recognizes the three as friends and asks the waiter to return $5 to the men.

The waiter is not only poor at mathematics but dishonest and instead of going to the trouble of splitting the $5 between the three he simply gives them $1 each and pockets the remaining $2 for himself.

Now, each of the men effectively paid $4, the total paid is therefore $12. Add the $2 in the waiters pocket and this comes to $14.....where has the other $1 gone from the original $15?

Ans : Though the initial bill was $15 dollars, one of the five dollar notes gets changed into five ones. The total the three men ultimately paid is $12, as they get three ones back. So from the $12 the men paid, the owner receives $10 and the waiter receives the $2. $15 - $3 = $10 + $2

2.You are trapped in a room with two doors. One leads to certain death and the other leads to freedom. You don't know which is which.

There are two robots guarding the doors. They will let you choose one door but upon doing so you must go through it.

You can, however, ask one robot one question. The problem is one robot always tells the truth ,the other always lies and you don't know which is which.

What is the question you ask?

Ans : Ask one robot what the other robot would say, if it was asked which door was safe. Then go through the other door.

Explanation : If we are asking the ques to robot A, either of the robots should say lie which means,

(Lie) robot B saying door B is safe,then robot A will say door A is safe = door A is safe

(True) robot B saying door B is safe,then robot A will say door B is safe = door B is safe