These two are my homework questions! Thanks a lot! Question 41:

These two are my homework questions! Please please help me with it!!! Thanks a lot!

Question 41:

(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?

Question 42:

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.