Check whether the following integers are multiplicative inverses of 3 mod 5.

Question

Check whether the following integers are multiplicative inverses of 3 mod 5.

a) 6

b) 7

Answer 1

a) 6 IS NOT a multiplicative inverse of 3 (mod 5) because 3 times 6 is 18, which IS NOT 1 (mod 5).

b) 7 IS a multiplicative inverse of 3 (mod 5) because 3 times 7 is 21, which IS 1 (mod 5).