There is an easy equation which can help:
1 brick = 1 kg + 1/2 brick
And so 1 brick is 2 kg heavy.

The equation is solved the right way, apart from one little detail. There must be stated
that x does not equal y, because there would be dividing by zero, which is not defined in
maths.

There can live maximum of 518 people in the town. By the way, it is clear that one inhabitant must by baldy, otherwise there wouldn’t be a single man in the town.

The original length of belt was 96 cm.

There are 4 cars 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 petrol 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.

Because there are 24 hours in one day, in one hour fills the first tap 1/48, the second tap
1/72, the third tap 1/96 and the fourth tap fills 1/6 of the reservoir. That is all together
(6+4+3+48) / 288 = 61/288. The reservoir will be full in 288/61 hours, which is 4 hours
43 minutes and about 17 seconds.

There are a few ways of solving this one. I like the following simple way of thinking.
The given situation (when the hour and minute hands overlay) occurs in 12 hours
exactly 11 times after the same time. So it’s easy to figure out that 1/11 of the clock
circle is at the time 1:05:27,273 and so the seconds hand is right on 27,273 seconds.
There is no problem proving that the angle between the hours hand and the seconds
hand is 131 degrees.

9 p.m.

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

There is a complicated way counting a sequence. Or simply knowing that if the fly is
flying the 2 hours still at the same speed of 75 km/h then it flies a distance of 150 km.

Of course, when the trains encounter, they will be approximately the same distance away from New York. The New York train will be closer to New York by approximately one train length because they're coming from different directions. That is, unless you take "meet" to mean "pefectly overlap".

Of course, adding seven to five makes twelve and not thirteen.