What occurs twice in a week, once in a year but never in a day?

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?

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

Which is the rope you never skip with?

I am green and found in the forest and have needles instead of leaves. What am I?
Hint 1: It can be used for Christmas decorations.
Hint 2: I have a strong, scent that is used in air fresheners.

What do you get if you add 2 to 100 four times?

You have a roll of cloth 1km long. You have a machine which cuts this roll into pieces of 10-meter-long cloth.

How long would it take for the machine to cut the roll if each cut took 4 secs?

What number comes next in this sequence:
7 8 5 5 3 4 4 _

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

What kind of band never plays music?