Interesting riddles....

[gdextreme]

I have a real interest in solving riddle so I decided to start a thread on riddles here at anandtech. Everyone is invited to post a riddle if he/she likes to do so. I'll start with an easy one:

1) There was a Buddhist monk who prayedto god everyday for 45min exactly. He noticed one day that his clock was broken. His student told him he could tell the monk when 45 min are over using 2 incense sticks. It is know an incense once lit stick lasts for exactly half an hour. Tell me how the student will know when 45 min have elapsed. The incense sticks are of non uniform thickness so upon cutting in half they will not last 15 minutes each.

 

[CalvinHobbes]

did he use the incense sticks to fix the clock?

 

[newb111]

He used the incense sticks to make a rudimentary sun-dial

 

[DingDingDao]

1) Light first stick on both ends (finished in 15 minutes)
2) Light second stick on one end (finished in 30 minutes)

 

[OCGuy]

He traded his incense for a watch.

 

[Nik]

Originally posted by: DingDingDao
1) Light first stick on both ends (finished in 15 minutes)
2) Light second stick on one end (finished in 30 minutes)

Ding.

 

[darkxshade]

Originally posted by: gdextreme
I have a real interest in solving riddle so I decided to start a thread on riddles here at anandtech. Everyone is invited to post a riddle if he/she likes to do so. I'll start with an easy one:

1) There was a Buddhist monk who prayedto god everyday for 45min exactly. He noticed one day that his clock was broken. His student told him he could tell the monk when 45 min are over using 2 incense sticks. It is know an incense once lit stick lasts for exactly half an hour. Tell me how the student will know when 45 min have elapsed. The incense sticks are of non uniform thickness so upon cutting in half they will not last 15 minutes each.

When both incense sticks are burned all the way through. You didn't ask how would the student know when 45 mins exactly has passed.

 

[darkxshade]

Originally posted by: DingDingDao
1) Light first stick on both ends (finished in 15 minutes)
2) Light second stick on one end (finished in 30 minutes)

While this is the logical and probably the right answer, how long would it take to light up an incense stick immediately after the first have burned out? Couldn't get 45 mins exact without a clock.

 

[gdextreme]

whoa 5 min and 5 replies already! Ding got it right. Newb111 : Interesting thought but he would need a clock to calibrate the sundial. One more riddle:
Just a level higher than the previous one

2) There are 3 light bulbs in a room and 3 switches outside the room. Each switch corresponds to a bulb. Now you are standing outside the room and you want to know which switch corresponds to which bulb. You can enter the room only once. You cant see the switches and the bulbs simultaneously from the doorway, and the bulbs are not fused, etc. How will you find which switch stands for which bulb?

 

[newb111]

Originally posted by: gdextreme
whoa 5 min and 5 replies already! Ding got it right. Newb111 : Interesting thought but he would need a clock to calibrate the sundial. One more riddle:
Just a level higher than the previous one

2) There are 3 light bulbs in a room and 3 switches outside the room. Each switch corresponds to a bulb. Now you are standing outside the room and you want to know which switch corresponds to which bulb. You can enter the room only once. You cant see the switches and the bulbs simultaneously from the doorway, and the bulbs are not fused, etc. How will you find which switch stands for which bulb?

Turn on A, leave it on for 5 min, turn it off.
Turn on B, leave it on.

Go in. The one that is off and hot is A, the one that is on is B, the one that is off and cold is C.

 

[gdextreme]

comeone darkshade don't ruin such a nice riddle . Time taken to light an incense stick should be assumed negligible

 

[Phoenix86]

Originally posted by: gdextreme
2) There are 3 light bulbs in a room and 3 switches outside the room. Each switch corresponds to a bulb. Now you are standing outside the room and you want to know which switch corresponds to which bulb. You can enter the room only once. You cant see the switches and the bulbs simultaneously from the doorway, and the bulbs are not fused, etc. How will you find which switch stands for which bulb?

Turn on switch one for several minutes.
Turn off switch one and turn on switch two.

Enter the room, feel the temp of the two unlit bulbs. The warm one is switch one, the lit bulb will be switch two, the cold unlit bulb is switch three.

 

[FP]

Originally posted by: gdextreme
whoa 5 min and 5 replies already! Ding got it right. Newb111 : Interesting thought but he would need a clock to calibrate the sundial. One more riddle:
Just a level higher than the previous one

2) There are 3 light bulbs in a room and 3 switches outside the room. Each switch corresponds to a bulb. Now you are standing outside the room and you want to know which switch corresponds to which bulb. You can enter the room only once. You cant see the switches and the bulbs simultaneously from the doorway, and the bulbs are not fused, etc. How will you find which switch stands for which bulb?

Turn on two lights, leave on for 45 minutes (by burning incense). Turn one off.

Go in room. On light corresponds to on switch. Warm light corresponds to the switch that was on but you turned off. Off/cold light is switch that was never on.

 

[gdextreme]

No offense newb111 but please don't reply if you have solved the riddle before. All credit goes to you if you solved it on your own.

 

[AstroManLuca]

Originally posted by: Nik

Originally posted by: DingDingDao
1) Light first stick on both ends (finished in 15 minutes)
2) Light second stick on one end (finished in 30 minutes)

Ding.

How do you light an incense stick from both ends? That doesn't seem physically possible.

 

[SSSnail]

Riddle fail, Buddhist monks don't pray to god.

 

[gsellis]

For 1, the glow of the second incense stick is bright enough for the student to read his watch.

 

[gdextreme]

3) There are 10 bags each containing 100 gold coins each. A genuine gold coin weighs 10gm each. A fake one weighs 9gm each. One bag contains all fake coins. Using an electroic weighing balance how do I check which bag has the fake coins if I am allowed to use the balance only once.

Don't reply if you have solved it before.

 

[2Xtreme21]

I won't reply because I know it, but this is a fun one.

 

[gdextreme]

Another Classic one. The answer to this on came to me almost insantaneously so its one of my favourites.

4) Captain Frank and some of the boys were exchanging old war stories.
Art Bragg offered one about how his grandfather led a battalion against a
German division during World War I. Through brilliant maneuvers he
defeated them and captured valuable territory. After the battle he was
presented with a sword bearing the inscription "To Captain Bragg for
Bravery, Daring and Leadership. World War I. From the Men of Battalion
Bravery, Daring and Leadership. World War I. From the Men of Battalion
." Captain Frank looked at Art and said, "You really don't expect
anyone to believe that yarn, do you?" What's wrong with the story?

 

[DingDingDao]

Originally posted by: gdextreme
Another Classic one. The answer to this on came to me almost insantaneously so its one of my favourites.

4) Captain Frank and some of the boys were exchanging old war stories.
Art Bragg offered one about how his grandfather led a battalion against a
German division during World War I. Through brilliant maneuvers he
defeated them and captured valuable territory. After the battle he was
presented with a sword bearing the inscription "To Captain Bragg for
Bravery, Daring and Leadership. World War I. From the Men of Battalion
Bravery, Daring and Leadership. World War I. From the Men of Battalion
." Captain Frank looked at Art and said, "You really don't expect
anyone to believe that yarn, do you?" What's wrong with the story?

Wouldn't have been called World War I at the time. Who knew there was going to be a second one?

 

[gdextreme]

5) How many times can you subtract the number 5 from 25 so that the result remains greater than -15 ?

 

[gdextreme]

very good DingDingDao! You are right.

 

[newb111]

Originally posted by: gdextreme
5) How many times can you subtract the number 5 from 25 so that the result remains greater than -15 ?

Infinite. 25 - 5 will always be greater than -15.

 

[nace186]

Originally posted by: gdextreme
3) There are 10 bags each containing 100 gold coins each. A genuine gold coin weighs 10gm each. A fake one weighs 9gm each. One bag contains all fake coins. Using an electroic weighing balance how do I check which bag has the fake coins if I am allowed to use the balance only once.

Don't reply if you have solved it before.

Take one coin from each bag and divide it in half.
Balance each half on the scale.
one side should be 1gm less.
Take one out from each side at a time, until it's balance.
The last one on the side that weight less is the fake coin/bag.