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 is the next number in this matchsticks series riddle?

What is the coolest letter in the alphabet?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

What has one letter and starts with an E?

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?

There are forty elephants and they have forty-fore heads. How can this be possible?

You have a roll of cloth 1km long. You have a machine which cuts this roll into pieces of 10-meter-long cloth.

How long would it take for the machine to cut the roll if each cut took 4 secs?

Forwards I am heavy, backward I am not. What am I?