What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

How many people must be gathered together in a room, before you can be certain that there is a greater than 50/50 chance that at least two of them have the same birthday?

Keyboard words are not in alphabetical order, Why?

Which tank will fill first?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

What number divided by 4 is the same as that number minus 4?

Irene killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.

A mathematics teacher took exams for his students. Out of the total students, 25% passed both the tests included in the exam. However, only 42% were able to clear the first test.

Can you find out the percentage of those students who passed the first test and also passed the second test?