Bulbs
Keep the first bulb switched on for a few minutes. It will get warm. So all you have to do then is ... switch it off, switch another one on, walk into the room with the bulbs, touch them and tell which one was switched on as the first one (the warm one) and the others can be easily identified ...

Ball in a Hole
All you have to do is pour some water into the pipe so that the ball swims up on the surface.

Water Brain Teasers

1. Fill the 5-litre bowl and overspill water to the 3-litre bowl, which you empty afterwards. From the 5-litre bowl overspill the 2 remaining litres to the 3-litre bowl. Refill the 5-litre bowl and fill in the 3-litre bowl (with 1 litre), so there stay the 4 required litres in the 5-litre bowl.

2. First fill the 9-litre bowl. Then overspill 4 litres to the 4-litre bowl (there are 5 litres in the 9-litre bowl afterwards) and pour out the water from the 4-litre bowl. And again overspill 4 litres to the 4-litre bowl and empty it. Then overspill the remaining litre to the 4-litre bowl but this time keep it there. Fill the 9-litre bowl to the top for the second time and overspill water to fill the 4-litre bowl to the top. Thus the required 6 litres stay in the 9-litre bowl.

3. Pour 1 litre from bowl A to bowl C. Thus 4 litres are left in the bowl A and bowl C is full (3 litres).
Pour 2 litres from bowl C to bowl B. Doing that you have full bowl B (5 litres) and there is 1 litre left in bowl C.

Weighing Brain Teasers

1. If there is only 1 bag with forgeries, then take 1 coin from the first bag, 2 coins from the second bag ... ten coins from the tenth bag and weigh the picked coins. Find out how many grams does it weigh and compare it to the ideal state of having all original coins. The amount of grams (the difference) is the place of the bag with fake coins.

2. Lay one red and one white ball on the left pan and one blue and the other white ball on the right pan. If there is equilibrium, then it is clear that there is one heavier and one lighter ball on each side. That’s why comparing white balls is enough to learn everything.
However, if at first weighing one side is heavier, then there must be a heavier white ball on that side. The next reasonable step is to compare the already weighed red ball and yet not weighed blue ball. After that, the character of each ball is clear, isn’t it?

Weird Money
This was just a trick question. One of the coins is really not a nickel because the nickel is the other coin.

Speeding Up
This one has no solution. Unless we include the relativity theory - time and space. But to keep it simple, you can't reach the desired average speed under the given circumstances.

Midnight
9 p.m.

Car In The Dessert
4 cars are needed, including the car with the important letter (which travels to the middle of the desert). Its empty tank must be filled to the top to get to the end of desert. The way between the military base (where the cars and gas is) and the middle of the desert can be divided into 3 thirds. 3 cars will go in their thirds back and forth and overspilling 1/3 of their tanks. This way the tank of the important car will be filled and the letter will be delivered.

Apples
4 kids get an apple (one apple for each one of them) and the fifth kid gets an apple with the basket still containing the apple.

Babies
The two babies are two of a set of triplets.

Albert Einstein Neighbours
Norwegian - yellow, Dunhill, water, cat
Dane - blue, Blend, tea, horse
Briton - red, Pall Mall, milk, bird
German - green, Prince, coffee, fish
Swedish - white, Blue Master, beer, dog