How many sides does a circle have?

What is next number in the pattern below:

131 517 192 123 ?

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?

If 2 workers can complete painting 2 walls in exactly 2 hours.

How many workers would be needed to paint 18 walls in 6 hours?

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?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

Why did Buffon take the goal with him after every Juventus match?

'S' refers to the number of seconds in a day and 'H' refers to the number of hours in ten years. Which quantity out of these two is greater?

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?