Count the number of triangles in the below picture?

Can you figure out the logic I used to decide the order of the following words:
gun, shoe, spree, door, hive, kicks, heaven, gate, line, den

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

Can you decipher the following common phrase?

T M C
A U O
H S M
W T E

What is the next number in this matchsticks series riddle?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

I hide my treasure in the ground, my tail is big and fluffy. If you spot me in a tree, please don’t call me scruffy. What am I?

An infinite number of mathematicians are standing behind a bar. The first asks the barman for half a pint of beer, the second for a quarter pint, the third an eighth, and so on. How many pints of beer will the barman need to fulfill all mathematicians' wishes?

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.