Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

A high school has a strange principal. On the first day, he has his students perform an odd opening day ceremony:

There are one thousand lockers and one thousand students in the school. The principal asks the first student to go to every locker and open it. Then he has the second student go to every second locker and close it. The third goes to every third locker and, if it is closed, he opens it, and if it is open, he closes it. The fourth student does this to every fourth locker, and so on. After the process is completed with the thousandth student, how many lockers are open?

In a particular village, only two barbershops exist.

The first shop has a handsome barber with a neat haircut who is handsomely dressed in clean clothes and is extremely humble with his body language. The place is clean and looks hygienic.

In the second shop, you can find a barber with shabby clothing. His hairs are weirdly cut and his clothes still have the stains from last night's dinner. The place is not clean as well and reeks a bit.

You visit the village for the first time and decide to get your haircut. Which barbershop will you like to go for that and why?

What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

What is the last thing you take off before bed?

What is the coolest letter in the alphabet?

There is something which is always coming but never arrives?

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

Prove that twice of ten is the same as twice of eleven.