Logic Riddle Collections

First, fill up the three litre jug. Pour the three litres into the five litre container. Refill the three litre jug and once again pour it into the five litre container until it is full. The three litre jug now contains one litre.

Empty the five litre container and then pour the one litre of water into it. Now, fill the three litre jug up again and pour it into the five litre container. The container will now contain the desired four litres.

No new riddle was posted to begin with.

Whim

Riddle #2: Three people with four hats
Very nice... now onto the 2nd riddle. This riddle looks long and complicated, but it is actually quite a simple story. Try to read the whole story:

Three people were caught by a wizard and was about to be turned into frogs. The three pleaded the wizard to spare their lives.

So the wizard, being a riddler, promise to free them if they can answer his riddle.

The three people were told to stand on a stairs (see pic below). The first person (A) stands at the top of the stairs, the second person (B) stands at the middle of the stairs, and the last person (C) stands at the bottom of the stairs.

__A__
|
|__B__
|
|__C__


All people is facing down. So A can see B and C. But B can only see C, but not A. C can see no one.

The wizard has a bag containing 4 hats: 2 whites, and 2 blacks. The wizard will randomly pick three hats and put it on top of each of the three people's head. Since the wizard randomly picks only 3 hats out of 4 hats, those three hats could be:

2 blacks, 1 white or
2 whites, 1 black

The wizard blinfolded the three people, then randomly draws 3 hats, then put each hat on their head, then open the blindfold. On the count of 3 seconds, if anyone from the three people can answer the color of the hat on top of his own head correctly, the three people will be free. If the answer is wrong, they will immediately die. So nobody will answer unless he is absolutely sure with his own answer.

1 second, nobody answered. 2 second, still nobody answer. Then suddenly the person in the middle (B) says the color of his own hat. He is confident his answer is correct and it's indeed correct.

The question is.... why or how come B can answer?

Since A didn't know the color of his own hat, the color of B's hat is different than the color of C's hat. If they were the same color, A would have known the color of his own hat.

Correct answer in general, but may confuse some others. May be clarified a bit further using color examples. Like what colors A see, and what color B see, and what color B says he is wearing.

If "b+c" have the same colour hat "a" will know his is the opposite colour.
If "a" says nothing, "b" will know "a" can see two different hats, so "b" knows his is the opposite of "c".

You need to solve it giving the colors too.

Whim

"b+c" have black, "a" knows he has white.
"b+c" have white and black, "b" knows if his was black "a" would have said white, so his must be white.

Too many smart people on this boad....

Here is third riddle for the day... if this one is answered very soon, next riddle will have to wait at least one day......

The third riddle is exactly the same story with the second riddle. However, this one instead of drawing 3 hats from a possible 4 hats, the wizard draws 3 hats from a possible 5 hats. The five hats are 3 whites and 2 blacks. Since the wizard draws only 3 hats randomly, the possibilites are:

3 whites or
2 whites 1 black or
2 blacks 1 white

The wizard blinfolded the three people, then randomly draws 3 hats, then put each hat on their head, then open the blindfold. On the count of 3 seconds, if anyone from the three people can answer the color of the hat on top of his own head correctly, the three people will be free. If the answer is wrong, they will immediately die. So nobody will answer unless he is absolutely sure with his own answer.

1 second, nobody answered. 2 second, still nobody answer. Then suddenly the person in the bottom (C) says the color of his own hat. He is confident his answer is correct and it's indeed correct.

The question is.... why or how come C can answer? And what color does C say he is wearing?

If B and C both had black, A would know he has white. Therefore, at least one of B and C are white. B and C are both aware of this.

If B saw black on C, then B would know he must have white (from above). Therefore, C has white. C is aware of this.

C correctly says he has white.

Correct answer by markr.... and very clear.....

Here's the fourth riddle.... very easy one....

If I travel from point A to B at a speed of 20 miles per hour, and then travel back from point B to A at a speed of 30 miles per hour. What is the average speed of my whole trip and explain how you got the number.

A to B is 30 miles journey takes 1 1/2 hrs
B to A is 30 miles journey takes 1 hr
total journey 2 1/2 hours total distance 60 miles
average speed 24 mph

Correct answer by carditel....

Here's the fifth riddle:

There is one big family trying to cross a river with only 1 boat. The boat can only load 2 objects, whether it's human or animal.

The family trying to cross the river consists of
1 dad
1 mom
2 sons
2 daughters
1 maid
1 fierce dog

If any of the son is left alone without the dad with him at the same place, the mom will kill the son.

If any of the daughter is left alone without the mom with her at the same place, the dad will kill the daughter

If the dog is left without the maid at the same place, the dog will kill everyone else.

Only the dad, the mom, or the maid can steer the boat.

Question: How can the whole family, including the dog, cross the river?

That's one violent family

I take the conditions as "if any of the sons are left with mom but without dad at the same place they will be killed", and likewise with mom and daughters. In other words sons can be left without dad for as long as mom is not around. Otherwise it is unsolvable. Here's my script:

1. Maid with Dog crosses (dad,s1,s2,mom,d1,d2 -- maid,dog)
2. Maid Returns (dad,s1,s2,mom,d1,d2,maid -- dog)
3. Maid with Daughter1 cross (dad,s1,s2,mom,dot2 -- dot1,maid,dog)
4. Maid returns with Dog (dad,s1,s2,mom,d2,maid,dog -- d1)
5. Mom with Daughter 2 cross (dad,s1,s2,maid,dog -- mom,d1,d2)
6. Mom returns (dad,s1,s2,mom,maid,dog -- d1,d2)
7. Mom and Dad cross (s1,s2,maid,dog -- dad,mom,d1,d2)
8. Dad returns (dad,s1,s2,maid,dog -- mom,d1,d2)
9. Maid and Dog cross (dad,s1,s2 -- mom,d1,d2,maid,dog)
10. Mom returns (dad,s1,s2,mom -- d1,d2,maid,dog)
11. Mom and Dad Cross (s1,s2 -- dad,mom,d1,d2,maid,dog)
12. Dad returns (dad,s1,s2 -- mom,d1,d2,maid,dog)
13. Dad and Son1 cross (s2 -- dad,s1,mom,d1,d2,maid,dog)
14. Maid and dog returns (s2,maid,dog -- dad,s1,mom,d1,d2)
15. Maid and son2 cross (dog -- dad,s1,s2,mom,d1,d2,maid)
16. Maid returns (maid, dog -- dad,s1,s2,mom,d1,d2)
17. Maid and dog cross ( -- dad,s1,s2,mom,d1,d2,maid,dog)

Correct answer by Lem.

Here is another one:

Four people try to cross a bridge at night. They only have 1 flashlight. The bridge can only have two people at one time.

First person can cross the bridge in 5 minutes. Second person in 10 minutes. Third person in 20 minutes. And last person in 25 minutes.

When a slower person cross the bridge together with a faster person, the time it takes to cross the bridge is the slower person's time. For example, if a 5 minute person cross the bridge with a 25 minute person, it takes 25 minutes to cross the bridge, since the faster person (the 5 minute guy) needs to accompany the slower person (the 25 minute guy) with flashlight.

The flashlight's battery can only last 1 hour. How will all 4 people cross the bridge?

1. 5 min person and 25 min person-------25 min
2. 5 min person returns----------------------5 min
3. 5 min person and 20 min person-------20 min
4. 5 min person returns----------------------5 min
5. 5 min person and 10 min person-------10 min

Total time 60 mins all persons have crossed.

That adds up to 65 minutes.

5/10: 10 min
5: 5 min
20/25: 25 min
10: 10 min
5/10: 10 min
Total is 60 minutes. The key his having the two slowest travel together.

I had had a hard day.

Wow.... nobody can answer this yet for so long?