Using Only Five 5's and any mathematical operator make sum as 37

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?

How can a man go eight days without sleep?

A man dies of old age on his 25 birthday. How is this possible?

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

A father's child, a mother's child, yet no one's son.

Who am I?

Fate has decided that you will only be pleased to meet me when you need me

Maybe that is why, when I am working, I start working

However annoying I may be to the regulars, the little ones are always inspired

I will always be waiting if you try to reach me

How many of you can guess my name, let me see

In a jungle where there are no street lights or any other artificial source of lights, I notice a black snake crossing the road.
How did I get sight of the snake?

I am the largest in my family of fifty.
The youngest of our family lives separately from the rest of the family and so do I.
I am regarded as harsh and tough.
I am so large, you cut me in two equal halves,
each half would still be larger than the second largest member of the family.
Who am I?

I look at you, you look at me, I raise my right, you raise your left. What am I?