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

The Puzzle: A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.
How far does the dog travel in 1 hour?

What has a bottom at the top?

John is selling fruits.
He sells grapes at $30, Dates $25, and a Wolfberry $45.
At what price does he sell fig?

PS: Logical Thinking

How far can you walk into the woods?

Which three-digit number, made of consecutive digits, like 567, is 2 less than a cube and 2 more than a square?

What does a man do only once in his lifetime, but women do once a year after they are 29?

Different lights make me strange by changing me into different sizes. What am I?

Once upon a time, there was a castle on a square island. The entire island was surrounded by a 14m wide trench. The Romans had wanted to invade the castle and had brought a few wooden planks along with them to facilitate themselves in crossing the moat. The planks were however found to be only 13m long.

The Romans still managed to cross the trench. How did they do it?

What is the next number in this series?

4,12,84,3612....