What word is represented by this rebus?

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

O T T F F S S ?

Transform the word THINK into BRAIN while changing only one letter at a time in a manner that each of the word in the process is a real word!!!

This was asked in an interview with Coa-Cola.

The interviewer has given me 100 marbles(50 white and 50 black) and two empty boxes.
He then told me that he will leave the room and i need to place all the marbles in two boxes.

And When he come back, he will draw a marble from any of the two box and if the marble is white I will be hired.

Also
* No box can be empty.
* All 100 marbles must be placed in one of the two boxes.

So what should I have done?

In the given figure, move three matchsticks so that the resulting figure contains two rectangles.

Distances from you to certain cities are written below.

BERLIN 200 miles

PARIS 300 miles

ROME 400 milesAMSTERDAM 300 miles

CARDIFF ??? miles

How far should it be to Cardiff ?

During which month do people sleep the least?

Different lights make me strange by changing me into different sizes. What am I?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Replace the question mark with the correct number.