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

There are three Athletes (John, Tarun and Harish) and their individual Coaches (Jacob, Meenaxi and Priyanka) standing on the shore.
No Coach trusts their Athlete to be near any other Coach unless they are also with them.
There is a boat that can hold a maximum of two persons.
How can the six people get across the river?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

I hide my treasure in the ground, my tail is big and fluffy. If you spot me in a tree, please don’t call me scruffy. What am I?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

With pointed fangs I sit and wait; with piercing force I crunch out fate; grabbing victims, proclaiming might; physically joining with a single bite. What am I?

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

I am lying and I always lie. Tell me whether I am lying or telling the truth.

There was a blind man. He had four socks in his drawer either black or white. He opened it and took out two socks. Now the probability that it was a pair of white socks is 1/2.

Can you find out the probability that he had taken out a pair of black socks ?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?