What work can one never finish?

The doctor advised his patient to take a tablet after every fifteen minutes. He gave him five tablets in total.

How much time will he take to have all the five tablets?

What number comes next in the series?

5 15 5 18 5 24 14 20 _

Here is a mathematical expression that also secretly tells a movie name. What movie is that?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

You board a train. The train will have to enter a tunnel soon. You are claustrophobic. Which place is the best for you to sit?

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.

Which digit occurred maximum times between the number 1 and 1000?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

Why is the Hole below a Lock?