Question

the unit digit of (1+9+9^2+9^3-----+9^2007​

Answer 1

Answer:

0

Step-by-step explanation:

Unit digit of 9^0 = 1,

Unit digit of 9^1 = 9,

Unit digit of 9^2 = 1,

Unit digit of 9^3 = 9,

Unit digit of 9^4 = 9, and so on.

So, 1 and 9 is repeated.

It is started from 0 and ended with, 2007, so there are total 2008 terms in this sum. So, 2008 is even. So, we can consider sum of only 2 digits for finding the last digit.

So, answer is 1 + 9 = 0.