What has many keys but can’t open a single lock?

Can you replace the question mark with the correct number?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

Can you count the number of lines in the below picture?

Two friends decide to get together; so they start riding bikes towards each other. They plan to meet halfway. Each is riding at 6 MPH. They live 36 miles apart. One of them has a pet carrier pigeon and it starts flying the instant the friends start traveling. The pigeon flies back and forth at 18 MPH between the 2 friends until the friends meet.

How many miles does the pigeon travel?

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

What is the difference between a jeweller and a jailer?

If you toss a coin 10 times and it lands heads up every time, what are the chances it will land heads up if you toss it again?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

What number comes next in this sequence:
7 8 5 5 3 4 4 _