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Josip has 4 toys - a car, a doll, a ball and a ship. He wants to put them on a line on a shelf. The ship has to be next to the car and the doll has to be next to the car. In how many ways can he arrange them so all the conditions would be fulfilled? 
Overseas Competition->Knowledge Point->Counting Modules->Questions Involving Enumeration->Enumeration
The car is in the middle of the ship and the doll. There are 2 ways to arrange the three toys, i.e. door-call-ship and ship-car-doll.  The last toy, the ball, can be placed on either of the 2 ends.  Therefore, there are 2 x 2 = 4 ways to arrange the toys. 