1) One family wants to get through a tunnel. Dad can make it in one minute, mom in two minutes, son in four and daughter in five minutes. Unfortunately, not more than two persons can go through the narrow tunnel at one time. Can they all make it to the other side if they have a torch that lasts only 12 minutes?
2) How many flowers do I have if all of them are roses except two, all of them are tulips except two, and all of them are daisies except two?
3) How many times can you subtract the number two from the number 32?
4) Why is it better for manhole covers to be round rather than square?
6) If you had a five-litre bowl and a three-litre bowl, and an unlimited access to water, how would you measure four litres exactly?
7) There is a room with no windows, doors, or any sort of opening. The walls are made of solid steel 10 feet thick, and you are trapped inside, left only with a saw and a table. How do you escape?
8) A couple has two kids, one of them is a girl. Assume safely that the probability of each gender is 1/2. What is the probability that the other kid is also a girl? Hint: It is not 1/2 as you would first think.
Solution:
1) First, mom and dad take two minutes. Dad comes back in three minutes, both children go to mom in eight minutes. Mom comes to dad in 10 minutes and they both get to their children in 12 minutes.
2) There can be two solutions. You can either have three flowers — a rose, a tulip and a daisy, or two flowers — a carnation and a geranium.
3) Once. After you subtract two from 32, you subtract 2 from 30, from 28, and so on.
4) You can turn a square manhole cover sideways and drop it down the diagonal of the manhole. You cannot drop a round manhole cover down the manhole. Therefore, round manhole covers are safer and more practical than square ones.
6) Fill the five-litre bowl and pour water into the three-litre bowl, which you empty afterwards. From the five-litre bowl pour the two remaining litres to the three-litre bowl. Refill the five-litre bowl and fill in the three-litre bowl (with one litre), so there stays the four required litres in the five-litre bowl.
7) This is a fantasy logic problem where words have alternate meanings (usually homonyms). You saw the table in half; but the two halves together make a whole (hole) and you crawl out through the hole.
8) 1/3. This is a famous question in understanding conditional probability, which simply means that given some information you might be able to get a better estimate. The following are possible combinations of two children that form a sample space in any family: Girl - Girl Girl - Boy Boy - Girl Boy - Boy
Since we know one of the children is a girl, we will drop the Boy-Boy possibility from the sample space. This leaves only three possibilities, one of which is two girls. Hence the probability is 1/3.
Source: brainden.com