What a wonderful world ....

It's hard to believe but it's true: If in the decimal representation of a fraction 1/p, where p is prime number and the length of a period is even then after adding the first half of the period with the last one we'll get only nines(!)

For example:

1/7  = 0.(142875) 142 + 875 = 999
1/13 = 0.(076923) 076 + 923 = 999