Problem: The sum to infinity of 71​+722​+731​+742​+… is:
Answer Choices:
A. 51​
B. 241​
C. 485​
D. 161​
E. none of these answers
Solution:
Rearrange the terms:
​s1​=71​+731​+⋯=1−(1/72)1/7​=487​s2​=722​+742​+⋯=1−(1/72)2/72​=482​s=s1​+s2​=163​​