7^1+7^2+7^3+.......+7^205. Find out how many numbers present which unit place contain 3?  Choose the correct choice:
A) 78 B) 51 C) 11 D) 27 E) 99
Units digits of first 4 terms are 7, 9, 3, 1. and this pattern repeats. So for every 4 terms we get one term with 3 in its unit digit. So there are total of 205/4 = 51 sets and each set contains one terms with 3 in its unit digit.   Ans is 51.   Answer:51
<result>B</result>
7^1+7^2+7^3+.......+7^205. Find out how many numbers present which unit place contain 3?