What four weights can be used to balance from 1 to 30 pounds?

I have Rs.50 and I spend it in the way as below.

Find the missing number in the sequence below:

At a party, there are five people and a whole round cake lying at the centre of the table. Only four people will make a cut and take their piece and the last one will get the remaining piece on the table. How can they make sure that everyone gets a 1/5th of the piece?

A few friends are enjoying their sea voyage in a boat full of apples. On the way, they felt hungry and thus decided to eat the apples. Together, they ate two dozen of apples. When they have eaten the apples, will there be any change in the water level?

A mathematician couple was having a Frappuccino in Starbucks sitting opposite to each other. Suddenly the guy noticed the text written on the paper in front of them and exclaimed that it was wrong. The girl denied it and said it is appropriate. Both are correct. What is written on the paper?

The day before yesterday I was 25 and the next year I will be 28. This is true only one day in a year. What day is my birthday?

There was a minor accident with a doctor's son but the doctor noticed no major injury. After the treatment, the father of that doctors son is sitting with the son of the doctor without the doctor being in the room.

How can this be possible?

In the picture given below, can you find out which digit will take place of the question mark?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?