Sunday, October 15, 2006

Few puzzles for you..

1. A father and his son are involved in a car accident, as a result of which the son is rushed to hospital for emergency surgery. The surgeon looks at him and says "I can't operate on him, he's my son". Explain.

2. A man is replacing a wheel on his car, when he accidentally drops the four nuts used to hold the wheel on the car, and they fall into a deep drain, irretrievably lost. A passing girl offers him a solution which enables him to drive home. What is it?

3. Three switches outside a windowless room are connected to three light bulbs inside the room. How can you determine which switch is connected to which bulb if you may enter the room only once?

4. There are 70 balls of same size. 69 Balls are of same weight and one is heavier. There is a two tray weighing balance. (compare the weight of A & B). You can use the balance 4 times and you should identify the odd one.

5. You have been given two threads. Both the threads takes 20 minutes to burn thru. The burning rate may not be uniform. (that is, the time taken is not proportional to the length). You have a match box and you need to identify 5 mintes with the two threads. How would you do it?

You can leave ur answers as comments..


Jayaram said...

Puzzle No 1: Surgeon is Mother

Joe Varghese said...

thats good. but 4 to go, Jayaram.

Jayaram said...

Puzzle No 3:Put the switch No 1 and kepp it for 5 minutes and switch off it.
and now switch on no 2 and enter in to the room Now u know the which bulb belongs to switch no 2; check for the other two bulb which one is hot, Hot bulb lights when u turn on when u put switch no 1, Now we know which is No 3 switch

Jayaram said...

Answer 3: Take the nuts of the spare wheel fix it to hold the wheel and put the damaged wheel inside the car

Jayaram said...

Last question is not clear ot me

joe said...

Puzzle 2: Good try..As you know, there may be only one nut on spare.. if that is the case, there is another way around..

Puzzle 3: Well done to change the duration from 10 minutes to 5 :)

Puzzle 5: That thread takes 20 min to fully burn from one side to another. But u cannot devide the length by four and take that time as 15 min, because the burning rate is not uniform.. Does it sound any better??

Joe Varghese said...


#1. Surgeon is Mother.


#2. Take one each other three wheels.


#3. Switch on the first one for 5 min. Switch it off and switch on the second.. Hot one is first, the one being on is the second and the other third.


#4. Divide the lot by three and weigh the two equal batch..

Divide the 70 into 25, 25 and 20 balls.. weigh between 25 and 25.. if they are equal, the heavier one is in the 20set.. else u know the 25set which has the heavier ball.. So u r left with max 25 balls..

divide the 25 into 9, 9 & 7.. follow the same and u r left with max 9 balls.

u get max 3 balls..

U have identified the ball


#5. If u start burning the thread from one side, it will take 20 min to get fully burned thru. So if you light it from both sides, it will take half the time.

So we light the first one from both sides and second one from one side. so when the first one gets burned, its 10 min over and there is 10 min left in the second thread. Light the second from the other end also at that instant and u can identify 5 minutes.