I’m tall when I’m young, and I’m short when I’m old. What am I?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

A prisoner is told: "If you tell a lie, we will hang you and if you tell the truth, we will shoot you." What did the prisoner say to save himself?

Count the number of triangles in the given picture.

A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 3 hours to fill the tank with the large inlet pipe. On the other hand, it takes 6 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 9 hours.

What fraction of the tank (initially empty) will be filled in 0.64 hours if all three pipes are in operation? Give your answer to two decimal places (e.g., 0.25, 0.5, or 0.75).

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

You see me once in June, twice in November, and not at all in May. What am I?

Can you identify the hidden rebus in the image below?