Question

Q.12
The unit digit of (1 +9+9^2 +9^3+ ........ +9^2009) is
(1) 0
(2) 1
(3) 9
(4) 3
​

Answer 1

=(9^0+9^1)+(9^2+9^3)+(9^4+9^5)+.......(9^2008+9^2009)

clearly this is the sum of the sum of even and odd power

that's why unit digital of this sum will be 0.