What is the unit digit of 15 + 25+ 35 + … + 205?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 0
Unit digit of 15 + 25+ 35 + … + 205
= 14n+1 + 24n+1 + .....204n+1 (form)
= 11 + 21 + 31 +.....201
= 1 + 2 + 3 +......20
= 20 × 21/2 = 210
Unit digit = 0