Can you make numbers like 24, using numbers 3,3,7 & 7 with any arithmetic operator?

Can you place six X (crosses) in below board without making three in a row in any way ?

A Detective reviewed the information they had on the case so far.

A lady named 'Caterina' was found shot and they already had a list of suspects - Ankit, Tarun, Harish, Manoj and Manish.
The killer is a fan of challenges him by leaving notes ad various places.
* The first was found in a toilet room.
* The second was found in an art room.
* The third was in a restroom.
* the fourth in an underwater room.
* The fifth at the no-smoking room.

All of the notes read the same thing, 'The clues are where you find the notes.' Yet, nothing was found at any place the notes were.
Detective the genius, immediately solved the case.
Who was the killer?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

2, 3, 5, 9, 17, _ What is the next number in the sequence?

What work can one never finish?

A red house is made out of red bricks. A yellow house is made out of yellow bricks. And, a blue house is made out of blue bricks. So, what is a greenhouse made of?

By what process could you make a 'Tea-Table' into food?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?