What is the unit digit in 15^100?  Options
A) 0 B) 1 C) 2 D) 3 E) 5

Rationale: unit digit in 15 ^ 100 = unit digit in [ ( 15 ^ 4 ) ^ 25 ] but unit digit in 15 ^ 4 = 5 unit digit 15 ^ 100 = 5 answer is e
Answer: E