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 time long back, there lived a king who ruled the great kingdom of Trojan House. As a part of the renovation of the kingdom to meet future security needs, he asked his chief architect to lay down a new play in a manner that all of his 10 castles are connected through five straight walls and each wall must connect four castles together. He also asked the architect that at least one of his castles should be protected with walls. The architect could not come up with any solution that served all of King's choices, but he suggested the best plan that you can see in the picture below. Can you find a better solution to serve the king's demand?

What does this rebus means ?

PROG WORKRESS

why number 8549176320 is one of a kind?

If,

6 / 7 = 2
3 / 9 = 7
8 / 2 = 6

Then

4 / 5 = ?

When it is alive we sing, when it is dead we clap our hands. What is it?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

I noticed one of the words in the oxford dictionary is spelled incorrectly. What about you?

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

I go up and I go down.
I go up towards the beautiful sky and down toward the green ground.
I am present tense.
I am past tense too
Children love me.

Who Am I?