Can anyone tell me a word in the English dictionary which has a silent 'z'?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

A pack of cards has 40 cards. You are blindfolded. Out of 40, 25 cards are facing down while 15 are facing up. You have been asked to divide this pack of cards into two decks - so that each deck contains an equal number of face-up cards. Remember, you are blindfolded.

How will you do it?

Can you decipher the below rebus?

PBLUESAISNUERSES

I am the fastest animal but cannot climb the tree. What am I?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?

John went to meet his friend Jacob, but when he was about to reach the main gate, John notices that Jacob had a mighty dog who was fastened to the tree. The chain is long enough that it allows the dog to reach the main gate.

How can the John reach the main gate?