I have eight fingers and two thumbs but I do not live. What Am I?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

In the below-given picture of a pretty girl, there is something wrong. Can you find out what it is?

All of Jacob's shoes are red except two.
All of Jacob's shoes are green except two.
All of Jacob's shoes are yellow except two.

How many shoes does Jacob have?

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.

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

I am Huge on Sunday and Saturday.
I am small from Tuesday to Thursday.
I do not exist on Monday and Friday.
Who am I?

Spot 5 differences in two Christmas tree below:

The ages of a father and son add up to 66.
The father's age is the son's age reversed.
How old could they be?
(3 possible solutions).