Transform the word THINK into BRAIN while changing only one letter at a time in a manner that each of the word in the process is a real word!!!

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

My cousin lives in one story house in Antarctica. His house is made the of-of sandstone. what is the color of stairs?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

The centre of the third figure is empty. What digit should fit inside?

You need to remove two matchsticks to make the below equation true. Can you do it ?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

People are waiting in line to board a 100-seat aeroplane. Steve is the first person in the line. He gets on the plane but suddenly can't remember what his seat number is, so he picks a seat at random. After that, each person who gets on the plane sits in their assigned seat if it's available, otherwise, they will choose an open seat at random to sit in. The flight is full and you are last in line. What is the probability that you get to sit in your assigned seat?

A bomb exploded in a room full of married couples and no one died. How?

Can you count the number of squares in the figure below?