These two are my homework questions! Please please help me with it!!! Thanks a lot!
(a) Use Fermat’s Little Theorem to show that, for every prime p other than 2 or 5, there is some positive integer r for which p|(10^r -1) .
(b) Is it true that, for all integers n, other than multiples of 2 and 5, there is some positive integer r for which n|(10^r -1) .
(c) What is the relationship between these questions and decimal expansions?
Let gcd(10, n)=1 , and let r be the smallest positive integer for which 10^r congruent to 1 (modulo n)
(a) Prove that 1/n has a recurring decimal expansion with period r.
(b) If n is prime, prove that r|(n-1).
(c) Find the periods of 1/13, 1/17, 2/31, and 1/47.