Which country gets ill every time?

You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes?

I am the beginning of everything, the end of everywhere. I'm the beginning of eternity, the end of time and space. What am I?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Can you count the number of quadrilaterals in the picture below?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

On a certain day, John celebrated his birthday. Two days later, his older twin brother Jacob celebrated his birthday.

Is this even possible? How can it be?

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

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211