When it's bad luck to meet a black cat?

You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes?

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?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

One absent-minded ancient philosopher forgot to wind up his only clock in the house. He had no radio, TV, telephone, internet, or any other means for telling time. So he travelled on foot to his friend's place a few miles down the straight desert road. He stayed at his friend's house for the night and when he came back home, he knew how to set his clock. How did he know?

What word is identified by the below rebus?

Your Your Your Your Your
Your Your Your Your Your

Arrange the numbers 1, 2, 3, 4, 5, 6, 7, 8 and 9 above and below the division line in a manner that the thus formed fractions equal to 1/3.

(You can use one number only once)

I travel all around the world but always stay in the corner. What am I?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?