Where logic? Intellect-battle description

For you, the game is presented, Where logic? Intellect-battle.
In this game you will be asked to undergo 4 rounds:
1) Find common: This tour presents 3 pictures, which combines something in common.
2) What is missing: This tour presents 1 picture, which obviously do not have any details of the.
3) They are young: This tour presents one picture on which famous people in youth.
4) Total formula: This tour presents 2 images, which when added to form the word.
In our game, there are 3 hints: Open one letter, Open the word, Help leading.