Question

What is the sum of the series?

Answer 1

@Hero can you he

Answer 2

*help me with this??

Answer 3

\[\sum_{n=1}^{20}(5-n)=5\sum_{n=1}^{20}1-\sum_{n=1}^{20}n\]
Recall some useful formulas:
\[\sum_{n=1}^k1=1+1+1+\cdots+1=k\cdot1=k\\
\sum_{n=1}^kn=1+2+3+\cdots+k=\frac{k(k+1)}{2}\]
So,
\[\sum_{n=1}^{20}(5-n)=5\sum_{n=1}^{20}1-\sum_{n=1}^{20}n=5(20)-\frac{20(21)}{2}=100-210=-110\]

Answer 4

thank you!

Answer 5

can you help with another?

Answer 6

@SithsAndGiggles