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?

One is to three as three is to five and five is to four and four is the magic number.
What is the pattern?

Why is the Hole below a Lock?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

Why 1729 is a magic number? Answer Logically.

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

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

Can you count the number of quadrilaterals in the picture below?

In a boat, the father of a sailor's son is sitting with the son of the sailor. However, the sailor is not present on the boat.

Can this even be possible?

In order to complete the racing competition, the Mexico racetrack has to submit its top and the most famous three horses to win the competition. Due to an electrical storm, all the records are cleared and no one knows which horse holds the record. They all look identical and it becomes even more difficult to differentiate the horses. There are 25 horses in the Mexico racetrack. But there can be only five horses at a time on the track. What will the least number of races that can be conducted to find out the three fastest horses?