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?

Make the seating arrangement of 10 children in such a way that there are 5 rows with 4 children in each row.

You have a basket containing ten apples. You have ten friends, who each desire an apple. You give each of your friends one apple.
Now all your friends have one apple each, yet there is an apple remaining in the basket.
How?

Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?

Can you start the fire using two pieces of wood?

If Bihan is 10, Anirudha is 20, and Kim and Seal are both 5, but Rikold is 10, how much is Kenniger by the same trend?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

Find the Odd One Out?
84129
32418
47632
36119
67626
72927

The barber of Town shaves all men living in the town. No man living in the town is allowed to shave himself. The barber lives in that town. Who then shaves the barber of the town?