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

I drive at an average speed of 30 miles per hour to the railroad station each morning and catch my train. On a particular morning, there was a lot of traffic and at the halfway point, I had averaged only 15 miles per hour. How fast must I drive for the rest of the way to catch my train?

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

By moving just one matchstick, you need to make the below statement true. Can you do it?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

In a rainy season, one day 3 huge ladies walked under a normal-sized umbrella.
The umbrella is not huge enough to accommodate all 3 ladies yet not a single lady got wet. Why?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

Take away the whole and some still remain. What is it?

No one wants to have it, but if one got it, he does not want to lose it. What is It?