How can you make number one disappear by adding something to it?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

When is the top of a mountain similar to a savings account?

How many bricks does it take to complete a building that is 15 feet wide, 30 feet deep, and 12 feet tall made of brick?

Remove two matchsticks to make the below equation correct.

It spends most of its day eating white, but when it’s quick enough, it gets to eat fruit and sometimes some blue things. It’s in a dark room, where the walls are blue, it runs from a ghost that roams the halls and haunts it all the time. What is it?

What has one letter and starts with an E?

In the given picture, you can find two letters missing. When two particular letters are placed in the missing spots, you get an eight-letter word while reading in the anti-clockwise direction. Can you find out the missing letters and the missing word eventually?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

Can you find the ages of a son, father and grandfather based on the following facts?
The sum of the ages of grandfather, father and son is 140 years.
The age of the son in months is the same as the grandfather in years.
The age of the son in days is the same as the father in weeks.