What does below rebus means ?

What is the coolest letter in the alphabet?

A train leaves from point A for point B at 80 mph. After half an hour, another train leaves from point B for point A at 60 mph.

Which of the trains will be farther from point A when they meet ?

Prove that twice of ten is the same as twice of eleven.

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

How many points are there on the globe where, by walking one mile south, then one mile east and then one mile north, you would reach the place where you started?

A man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.

Find the missing letter in the last circle logically in the given below picture.

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?