If eleven plus two equals one, what does nine plus five equal?

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?

Why do we preferably have round manhole covers and not square ones?

Before Mount Everest was discovered, what was the highest mountain in the world?

Christina, Allison and Lena are 3 daughters of John a well-known Mathematician, When I asked John the age of their daughters. He replied "The current age of her daughters is prime. Also, the difference between their ages is also prime."

How old are the daughters?

I am written with two letters.
I said with the one.
I usually am seen with the two.

Who am I?

I am soft and cuddly that soothe your heart. But, If you pick my last name I am going to tear you all apart. Who am I?

What goes up but never comes down?

What is the difference between a jeweller and a jailer?

You have two bottles of pills marked with labels A and B. The pills are identical. The doctor has asked you to take one A pill and one B pill daily. You cant take more or less than that.

While taking out the pills one day, you took out one pill from A and by mistake took out two from B. You have no idea which pill is which now.

You cant throw away the expensive pills. What will you do now?