What work can one never finish?

Find out a multi-digit number that if multiplied by the number 9 or any of its multiplications products (i.e. 18, 27, 36, 45,..) will result in the multiplication factor repeated (n) number of times.

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

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?

I am eight letters long - "12345678"
My 1234 is an atmospheric condition.
My 34567 supports a plant.
My 4567 is too appropriate.
My 45 is a friendly thank-you.
My 678 is a man's name.

What word am I?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Why do you find that most of the buildings are deprived of the 13th floor?

In the picture given below, can you find out which digit will take place of the question mark?

A worker is to perform work for you for seven straight days. In return for his work, you will pay him 1/7th of a bar of gold per day. The worker requires a daily payment of 1/7th of the bar of gold. What and where are the fewest number of cuts to the bar of gold that will allow you to pay him 1/7th each day?

Keyboard words are not in alphabetical order, Why?