Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

I have lakes with no water, mountains with no stone and cities with no buildings. What am I?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

There are five vowels (a, e, i, o, u) in the English language.
Can you tell us a word that contains all these vowels?

What do you answer even though it never asks you questions?

Which of the following words don't belong in the group and why?
CORSET, COSTER, SECTOR, ESCORT, COURTS

In the addition below, all digits have been replaced by letters. Equal letters represent equal digits and different letters represent different digits.
ABCABA
BBDCAA
ABEABB
ABDBAA
------- +
AAFGBDH
What does the complete addition look like in digits?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Make a sentence consisting of three words that have the whole alphabet.