Puzzles to puzzle you
1. Circle the Earth:
The circumference of the Earth is approximately 40,000 kilometers, and Lekha has just woven a long rope that circles the Earth exactly, touching the ground at all locations.
Pari comes along at night, as a practical joke, and adds just 10 meters (1/100th of a km) to its length, so if Lekha tries to actually use it to encircle the earth, it will no longer touch the ground but will be at a height h above the ground.
How far above the ground will it be? Will h be large enough so a flea could go under it, or a dog, or even you? Can you find out?
2. What's the probability?
A 1-metre stick is broken into two pieces at random. What is the length of the shorter piece, on average?  
3. Non-linear candles
In front of you are several long fuses. You know they burn for exactly one hour after you light them at one end. But here's the catch: the entire fuse does not burn at a constant speed. For example, it might take five minutes to burn through half the fuse and fifty-five minutes to burn the other half. How can you measure exactly three-quarters of an hour of time using these fuses?
4. Alphabet multiplication
Here is a multiplication problem:
ABCD × E = DCBA
You are told that A,B,C,D, and E all represent different digits. Can you find out what they are?
From mathsisfun.com