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Sunday, June 4, 2017

Riddles 10 [With Answers]

Puzzle - 1:

A car has to carry an important person across the desert.

There is no petrol station in the desert and the car has space only for enough petrol to get it half way across the desert.

There are also other identical cars that can transfer their petrol into one another.

How can we get this important person across the desert?

Answer: We need 4 cars (including the car with the important person).

All 4 cars start full.

At 1/6th of the way, all cars are 2/3rds full. One car sacrifices itself and fills up two of the other cars. Two cars are now full, one is 2/3rds full. (An empty car is left behind.)

At 2/6th of the way, two cars are 2/3rds full. One car is one third full, and sacrifices itself to fill up one of the other cars. One car is now full, one is 2/3rds full. (An empty car is left behind.)

At half way, one car is 2/3rds full. One car is one third full, and sacrifices itself to fill the other car, which is now full and can make the other half of the journey.

Puzzle - 2:

Joey leaves his house in the morning to go to day camp.

Just as he is leaving his house he looks at an analog clock reflected in the mirror.

There are no numbers on the clock, so Joey makes an error in reading the time since it is a mirror image. Joey assumes there is something wrong with the clock and rides his bike to day camp.

He gets there in 20 minutes and finds that just as he gets there the day camp clock has a time that is 2 1/2 hours (2 hours and 30 minutes) later than the time that he saw in the mirror image of his clock at home.

What time was it when he got to day camp?

(The clock at camp and the clock at home were both set to the correct time.)

Answer: First subtract 20 minutes from 2 1/2 hours to compensate for his 20 minute bike ride to give a difference of 2 hours and 10 minutes.

To be a "Mirror Effect" it must be mirrored around 12 o'clock (when the hands are straight up), or around 6 o'clock (when the hands are pointing up and down), as we know he left in the morning, it must be 6 o'clock.

So, divide that 2 hours and 10 minutes by 2 and this will give you the center-point (65 minutes) for compensating for the mirror.

By adding that 65 minutes to 6 o'clock you get the time he left home (7:05), and the time he saw in the mirror (4:55).

Furthermore, by re-adding the 20 minutes from when he left (7:05), you get what time he got to camp (7:25).

Puzzle - 3:

In front of you are several long fuses.

You know they burn for exactly one hour after you light them at one end.

But the entire fuse does not burn at a constant speed. For example, it might take five minutes to burn through half the fuse and fifty-five minutes to burn the other half.

With your lighter and using these fuses, how can you measure exactly three-quarters of an hour of time?

Answer: Light both ends of one fuse.

At the same time light one end of a second fuse.

The first fuse will finish in half an hour.

At that point the second fuse will be half done (in time, not necessarily in distance) and you immediately light its other end. The second half hour will now take only quarter of an hour.

Total time: half an hour plus quarter of an hour equals three-quarters of an hour.

Puzzle - 4:

You have two straight lengths of wood.

How can you cut one of them so that one of the three pieces is the average length of the other two?

Answer: Put the two pieces end to end in a straight line
Then the average length of the three cut pieces has to be one third of this total length.

So we simply cut one third of the way along the longer piece.

Puzzle - 5:

A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.

How far does the dog travel in 1 hour?

Answer: 10km. Because the dog's speed is 10 km/h.