Answers

2014-07-19T19:00:04+08:00
Like this ? There are 4 primes smaller than 10, 25 smaller than 100, 168 smaller than 1000, 1230 smaller than 10000. You see that the fraction of primes goes down quickly. 

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2014-07-20T11:20:22+08:00
Combination like numbers and letters. Study how the car plates happen.
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