I have branches, but no fruit, trunk or leaves. What am I?

Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209

Find the next number in the sequence

5 12 24 36 ?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

Can you replace the question mark with the correct number?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

You and your two friends are working in a multinational company. How can you three find out the average salary of you all without disclosing your own salary to the other two?

Today is John's birthday.
A year ago, John had five candles and he lit all the candles except the one at the last.
Now he is going to light all the candles.

How old is John Today?

(He is not five today.....)

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

What is the largest number you can write with just 3 digits?