What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

What do you get if you add 2 to 100 four times?

A finger goes in me. You fiddle with me when you're bored. The best man always has me first. What am I?

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

A gardener planted the Lemon trees in a mathematical ordered way (i.e. he planted a tree in rows).
He created a total of 19 rows of trees.

Note: There should be more than 2 trees to count as a row.

What is the minimum number of trees required by the gardener to have 19 rows of trees?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

I have branches, but no fruit, trunk or leaves. What am I?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

I am first found in caves, now prolific online; I am a depiction, a drawing, a symbol, or sign. I will convey whichever mood you could wish; or for that matter, a fist, flask, or fish. What am I?

A boy purchased a book from a bookkeeper and gave him $100.
The cost of the book is $50 but the bookkeeper has no change, so he gets the change from the next shop and returns the boy his $50.

After some time the next shopkeeper came with the $100 note and told the bookkeeper that the note was a fraud, so he took the money back.

How much loss did the bookkeeper face?