What work can one never finish?

Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

Can you find out which options fits best with the missing column?

What occurs twice in a week, once in a year but never in a day?

Can you find a number that lies one third of the distance between 1/3 and 2/3?

What jumps when it walks and sits when it stands?

A chicken farmer has figured out that a hen and a half can lay an egg and a half in a day and a half. How many hens does the farmer need to produce one dozen eggs in six days?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?

In the addition below, all digits have been replaced by letters.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?