Puzzles - 1

Here we r not talkin' of the Verb Puzzle, but about the Noun PUZZLE!

Puzzle, as defined by Google, is

A game, toy, or problem designed to test ingenuity or knowledge.

So, here r some great problems i came across in my life to test ingenuity of an above average human being.

1. There are 9 Gold coins. Out of which one is fake i.e weight is less or more (i repeat, u don't know whether d fake coin is heavier or lighter). How many minimum number of weighings are required to find fake coin? 

2. A certain street has 1000 buildings. A sign-maker is contracted to number the houses from 1 to 1000. How many zeroes will he need?

3. 25 - 2 = 3
100 x 2 = 20
36 / 3 = 2

What is 144 - 3 = ?

P.S.: Answers in my next Blog!