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?

Can you solve this picture maths equation?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

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?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

What is the Surname of Barbie Doll?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?