Answer to Riddle 8 - The Egg Problem

You peel the egg and stand it upright on its flat end.
NOBODY ASKED YOU NOT TO PEEL IT. 

Answer to Riddle 9 - Quarter Problem

Oh, no, it is impossible. Oh, yes, it is possible. Take your dollar bill, fold in half widthwise and keep it on the table with both its sides making a small triangle (opening at the other edge or like an accordion). Now you can balance the quarter towards its angle side.

Answer to Riddle 10 - Ten Pennies Problem

If you see the diagram below, you can easily understand which three pennies to move to look triangle pointing at the opposite sides. Yes, the three pennies of the tip of the triangle.

O                                                    O
       O                                    O
O             O                       O           O
       O             O         O           O
O             O                        O           O
        O                                       O
O                                                      O

Answer to Riddle 11 - Six Glasses Problem

You may pour the second glass water in the center empty glass. Thus the six filled and empty glasses  will be arranged alternatively. 
NOBODY SAID THAT POURING WAS ILLEGAL.

Answer to Riddle 12 - Problem of Separation

What did you say? One cannot do it? Oh it is very easy, just think again and you can do it. First take a magnet and separate all the iron powder, then fill the pot with water - salt will melt in the water, sand will settle down in the bottom and saw dust will float on the water. Take a sieve and take out saw dust in it. Pour the water slowly in some other pot, it is salted water. To take out the salt from water, boil it until only salt remains. Sand is settled at the bottom, dry it in sunshine.

Answer to Riddle 13 - Problem of Transportation

If he takes lion with him, goat eats the grass, if he takes the grass with him, the lion eats the goat. So first he will take the goat with him and leave him on the other side of the river (lion doesn't eat grass). Then he will take the lion and leave him on the other bank of the river and bring back the goat with him. Then he will take grass and leave the goat on the first bank of the river. He will drop the grass with lion and come back to take his goat.

Answer to Riddle 14 - The Problem of Tide

None. Are you surprised? But this is the answer, why? The boat rises with the tide.