If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

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?

You can hear me, but you can't touch or see me.

What am I?

If 21x = 79x, what is the value of x?

A plane crashed between the border of Mexico and America. Where do you bury the survivors?

If you had an infinite supply of water and 5-quart and 3-quart pails, how would you measure exactly 4 quarts? What is the least number of steps you need?

It is always ahead of me yet I can never see it. What is it?

Using eight eights and addition only, can you make 1000?

Can you replace the X (both small and big x) with the numbers between 1 to 19 such that all the rows of 3 numbers between X (big x) sum to 23?

I was born in a small house and I live in it all alone. No windows and no doors have been assigned to my house. The only way I can go out is by breaking through the walls of my house.

Who am I?