wolfgang

You have 8 coins that all look  exactly the same, two of them are fake,one of these two fake coins is 0.1gm more than a normal coin, whereas the second coin is 0.1 gm less than a normal coin.

 With howmany weighings can you find them out  using a balance scale?

Can you make a square  using two circles?

Suppose that we have on the moon a space station which is the only source of fuel and on it there are  unlimited number of identical spaceships,  We want to send one of them  to Mars, each spaceship has a fuel capacity to allow it to fly exactly 1/4 way  to Mars (without fuel the spaceship will miss its direction and may explode!).
Each spaceship has the ability to refuel  by a second spaceship through a specific connection between them without loss of speed . What is the fewest number of spaceships necessary to  accomplish this mission  without losing any one of them?

Note:1- Each spaceship must have enough fuel to return safe to the base space station .

         2- The time and fuel consumption of refueling can be ignored. (so we can also assume that one spaceship can refuel more than one spaceship  at the same time).

Take the numbers 2 to 9  to make three numbers each of three digits, so that the first number is twice the 2nd number , and the 2nd is twice the 3rd number.

Each number should come only once except for one number should come twice.

Zero is not included.

what are the three numbers?

Eight persons having numbers on their backs( 1 to 8) were standing randomely behind each other in a straight raw( so that the first person can see nothing,while the others,each one can see only the number of the person standing infront of him), each one has a mini cube in his hand containing one number,from 1 to 8 at random, no one of them know neither the number on his back  nor the number inside his cube, but the number inside the cube for each person is either lager than or smaller than the number on his back by 1.

They have to enter another room,starting from the last one,,, in the other room there is a rectangular table drawn on it 8 squares in a straight raw, in each square there is a number, 1 to 8.

Each person when enters the room ,he should put his cube on the table( according to previous plan ),and get out through another door, and only the last person is allowed to put all the cubes inside  the squares so that they should match each other,i.e. the 1st square should have number 1, 2nd square number 2...and so on.

Any kind of comunications between them is forbidden.

They are allowed to set a plan before starting the mission.

What is the PLAN ?