Question

5. Expla in why 4 is or is not a multiplicative inverse mod 10 of 7.

Answer 1

4 is not. (3 is)

Explanation:

A number is the multiplicative inverse of 7 (mod 10) if the product mod 10 is 1.

7 × 4 mod 10 = 28 mod 10 = 8 . . . . not 1