Why do we preferably have round manhole covers and not square ones?

What is the next number in this series?

4,12,84,3612....

Replace the question mark with the correct number.

Can you make the number 24 by utilizing the numbers 1, 3, 4 and 6? You must use one number only one time and you can use mathematical operation symbols anytime anywhere.

Alpha is Beta's sister.

Gamma is a Beta mother.

Delta is Gamma's father.

Tango is Delta's mother.

Then,

How is Alpha related to Delta?

What type of tree can I carry in my hand?

You are given four results as below:
1111 = F
2222 = E
3333 = T
Then, can you find out how to code 4444?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

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

There is a place where if I stand up straight, I will still be considered sideways.