Which alphabet letter is a question?

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.

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Why do people go to bed?

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 number 8549176320 is one of a kind?

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.

My first is in chocolate but not in ham. My second is in cake and also in jam. My third at tea time is easily found. Altogether, this is a friend who is often around. What is it?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?