Brain Teasers


Time Across The Bridge

4 people need to cross a narrow, dangerous bridge late at night. They have a total of 1 flashlight between them. Only a maximum of 2 people can cross the bridge at any one time. With such a dangerous bridge, the people crossing the bridge must always have the flashlight with them. Each person moves at a different speed, and thus any two people must travel at the speed of the slowest. The respective speeds of the 4 people are 10mins, 5mins, 2mins and 1min. What is the shortest time that everyone can safely cross the bridge. Before you look at the answer, it is less than 19 mins, but why?

10, 5, 2, 1 ======== Otherside

2 Fuses

I have a box of matches and 2 fuses, that will burn for one hour each. How can I tell when 45 minutes have completed. Note, you cannot bend the fuses nor mark the fuses in anyway, as they are different lengths and burn at different speeds. you can just guarantee that they will burn for 1 hours each.

2 Bicycles and a Bumble Bee

2 Bicycles are 20 kms apart. They each start heading towards each other at 10kms per hour. There is a bumble bee on one of the bikes. When they start, the bumble bee flys at 20km per hour to the other bike and then back again and so on, until the 2 bikes have reached each other. How far does the bumble bee fly?

2 Rows of 4 Coins

I have 6 coins, laid out in 2 straight lines with one coin joining them. Ie, there are 4 coins in one line and 3 in the other. Move only one coin and make 2 straight lines of 4 coins. You may not introduce any new coins. Eg.

($) ($) ($) ($)
($)
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In your cellar there are three light switches in the OFF position.
Each switch controls 1 of 3 light bulbs on floor above. You may move
any of the switches but you may only go upstairs to inspect the bulbs
one time. How can you determine the switch for each bulb with one
inspection?


There are 3 black hats and 2 white hats in a box. Three men (we will call them A, B, & C) each reach into the box and place one of the hats on his own head. They cannot see what color hat they have chosen. The men are situated in a way that A can see the hats on B & C's heads, B can only see the hat on C's head and C cannot see any hats.

When A is asked if he knows the color of the hat he is wearing, he says no.
When B is asked if he knows the color of the hat he is wearing he says no.
When C is asked if he knows the color of the hat he is wearing he says yes and he is correct.

What color hat and how can this be?

There is no play on words and there are no tricks. If I used had instead of has
it is purely accidental.


A census taker approaches a house and asks the woman who
answers the door,"How many children do you have, and what
are their ages?"

Woman: "I have three children, the product of their ages are
36, the sum of their ages are equal to the address of the
house next door."

The census taker walks next door, comes back and says, "I
need more information."

The woman replies, "I have to go, my oldest child is
sleeping upstairs."

Census taker: "Thank you, I have everything I need."

Question: What are the ages of each of the three children?

 

 

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