Question

The units digit of $7^{2019}$ is

• A. 7
• B. 9
• C. 3
• D. 1

Answer 1

Answer:

C. 3

(7,10) = 1

$7^{\phi(10)}≅1(mod10)$

$7^4≅1(mod10)$

$7^{2019}=7^3(mod10)≅3(mod10)$