What English word has three consecutive double letters?

Three cars are driving on a track that forms a perfect circle and is wide enough that multiple cars can pass anytime. The car that is leading in the race right now is driving at 55 MPH and the car that is trailing at the last is going at 45 MPH. The car that is in the middle is somewhere between these two speeds.
Right now, you can assume that there is a distance of x miles between the leading car and the middle car and x miles between the middle car and the last car and also, x is not equal to 0 or 1.
The cars maintain their speed till the leading car catches up with the last car and then every car stops. In this scenario, do you think of any point when the distance between any two pairs will again be x miles i.e. the pairs will be x distance apart at the same time ?

A thief enters a store and threatens the clerk, forcing her to open the safe. The clerk says, “The code for the safe is different every day, and if you hurt me you’ll never get the code.” But the thief manages to guess the code on his own. How did he do it?

What is the next number in the series?

15 29 56 108 208 ?

I don't get anymore wetter, no matter how much rain falls on me.

Count the squares in the matchstick puzzle below?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

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

What does below chemistry rebus means?

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

What am I?