If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

The more of this there is, the less you see. What is it?

An office is divided into 8 cubicles. How many of the cubicles are painted if only 1/8 of the cubicles are painted?

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

Can you find the key in the picture below?

Spot the cat in the picture below

What does this rebus mean?

O
N
C
E
TIME

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?

What 5-letter word typed in all capital letters can be read the same upside down?

Can you count the number of squares in the figure below?