Question

use fermat's little theorem to find the unit digit of 3^100, use p=5

Answer 1

if i remember it right, \[a^{p-1}\cong 1 \pmod p\]

Answer 2

with p=5, you get \[3^4\cong 1\pmod 5\]

raise both sides to 25 and you get the answer to the problem