5 + 5 + 5 + 2 × 5^2 + 2 × 5^3 + 2 × 5^4 + 2 × 5^5 + 2 × 5^6 + 2 × 5^7 =
Pick:
A) 5^9
B) 5^7
C) 5^10
D) 5^8
E) 5^11
We have the sum of 9 terms. Now, if all terms were equal to the largest term 2*5^7 we would have: sum=9*(2*5^7)=18*5^7=~5^9, so the actual sum is less than 5^9 and more than 5^7 (option B) as the last term is already more than that. So the answer is clearly D.   Answer: 5^8
<result>D</result>
5 + 5 + 5 + 2 × 5^2 + 2 × 5^3 + 2 × 5^4 + 2 × 5^5 + 2 × 5^6 + 2 × 5^7 =