Hello, I'm having some issues solving some apparently 'basic' summation problems where they give you a couple summations and you derive the missing summation. I would appreciate any help not only solving this particular question but actually understanding the situation. Thanks! 1. The problem statement, all variables and given/known data Suppose: 113 [tex]\Sigma[/tex] ak = 641 k=9 and 507 [tex]\Sigma[/tex] ak = 2091 k=70 and 113 [tex]\Sigma[/tex] ak = 130 k=70 Then: 507 [tex]\Sigma[/tex] ak = ? k=114 2. Relevant equations I think everything relevant is provided above. 3. The attempt at a solution I have absolutely no idea how to start. I've googled summation problems and read quite a bit more than what is in my text. I keep finding information on what I can already do; problems like: 10 [tex]\Sigma[/tex] a-20 = ? k=1 Where a is a constant instead of having the 'k' subscript so you can take (10-(1-1)) * (a-20). Although, for some reason sticking the subscript onto a throws me off completely. Any suggestions are welcome. Thank you for your time!