Replace the question mark with the number below given a simple math problem.

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

Which is heavier: a ton of bricks or a ton of feathers?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

In the following series, a set of numbers is progressing with a particular pattern. Can you deduce that pattern and find the missing set?

(2 + 6), (21 + 6), (58 + 6), (119 + 6), ___

Below, you can see three complete equations and one incomplete. Based on the three complete ones, can you complete the incomplete one?

5 $ 4 $ 3 $ 9 = 4215
6 $ 9 $ 2 $ 6 = 3816
4 $ 7 $ 3 $ 3 = 1122
7 $ 2 $ 7 $ 4 = ____

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?

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

You and your two friends are working in a multinational company. How can you three find out the average salary of you all without disclosing your own salary to the other two?

John and Jenni are a married couple. They have two kids, one of them is a girl. Assume safely that the probability of each gender is 1/2.
What is the probability that the other kid is also a girl?

Hint: It is not 1/2 as you would first think.