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

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

You’re out on the water and see a boat filled with people. You look away for a second and look back again, but this time you don’t see a single person on the boat. Why? Hint: The boat did not sink.

In a supermarket, there is an intelligent glass pane before a refrigerating unit. This glass pane allows cherries and apples through it but does not allow grapes and Orange to pass through it.

Can you identify the rule that the glass pane is following?

A boy and a girl are sitting on the porch.
"I'm a boy," says the child with black hair.
"I'm a girl," says the child with red hair.
If at least one of them is lying, who is which?

The doctor prescribed you to take one pill from the bottle every half an hour. The bottle is now left with only three pills.

How long do you think you have before you run out of pills?

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

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

"That Restaurant always remains crowded. This is the reason why nobody goes there".

Can you find a flaw in this statement?

That attorney is my brother, testified the accountant.

But the attorney testified he didn't have a brother.

Who is lying?