Why Aeroplane windows are round?

Why is a river so rich ?

How do you go from 98 to 720 using just one letter?

Which is the correct shadow of the bird?

You stand in front of two doors. A guard stands next to each door. You know the following things: one path leads to paradise, the other leads to death. You cannot distinguish between the two doors. You also know that one of the two guards always tells the truth and the other always lies. You have permission to ask one guard one question to discover which door leads to paradise. What one question would you ask to guarantee you enter the door to paradise?

The below given figure comprises of a pattern through which you can determine the missing letter. Can you push your mind to find the pattern and add the missing letter?

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.....)

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

Find the next number in the series.
1 10 24 43 67 ?

Complete the table series riddle by finding the number that can replace "??".