What occurs twice in a week, once in a year but never in a day?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

There are three identical triplets sisters. Demi is the oldest of them all and she always speaks the truth. Diana is the next one who is a liar always. Drew, the youngest of them all speaks both truth and lies randomly.

On a rainy day, a family friend Victor visited them. Since there were starkly identical, he was not able to recognize them. Thus to clarify, he asked one question to each one of them.

He started with the one standing on the left and asked, 'Which sister is in the middle of you three?' She answered, 'That's Demi.'

Then, he asked the one standing in the middle, 'What is your name?' She answered, 'I am Drew.'

Finally, he asked the one standing on the right, 'Who is standing in the middle?' She answered, 'She is Diana.'

Victor was left baffled. He asked the questions three times and received different answers every time.

Can you tell who was who?

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.

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

What has many teeth, but cannot bite?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

I am a normal creature, but I have five hands. I can even have more but even then I will be considered normal.

Who am I?

Solve the puzzle by telling what does below picture means.

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?