Name one eight-letter word with 'kst' in the middle, 'in' the beginning, 'and' at the end.?

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.

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

One night, Louis and Adam were sitting together. Adam was watching a movie while his wife Louis was reading a mystery book. Suddenly the power went out and Adam decided to go to bed, but strangely Louis kept on reading. There was no artificial light around, so Louis kept on reading. How come?

'Ferrari driver' easily beats the 'force driver' in a two-car race. How did Indian newspapers truthfully report so to look as a 'force drive' had outdone the 'Ferrari driver'? Think!!!

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?

Wednesday, Steve and Pam go to a restaurant to eat lunch. After eating lunch, they pay the bill. But Steve and Pam do not pay the bill. So…who does?

I was speeding and ran through a stop sign, yet two traffic officers who were there do nothing about it.

why?

Which tank will fill first?