Why is Saturday stronger than Monday?

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

In two decks of cards, what is the least amount of cards you must take to be *guaranteed* at least one four-of-a-kind?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

Twenty frogs are sitting on a log floating on the surface of a river. Two of them decide to jump off into the water.

How many frogs are there on the log at this moment?

Can you find a seven digit number which describes itself. The first digit is the number of zeros in the number. The second digit is the number of ones in the number, etc. For example, in the number 21200, there are 2 zeros, 1 one, 2 twos, 0 threes and 0 fours.

Be active and find the killer in the picture Riddle below.

What seven-letter word has hundreds of letters in it?

I always drive my customer away.

Who am I?

Who has married many women but was never married?