A math word problem?

Question

If L represents the sum of the first three terms of a geometric sequence in which the second and third terms are 1 and 3, respectively, and M represents the sum of the first three terms of a geometric sequence in which the second and third terms are 3 and 1, respectively, then what is M-L?

Answer 1

Justin,

 

For sequence #1: Second term is 1 and third term is 3 so the first term will be 1/3 (Ratio term(n+1)/term(n) = 3)

 

For sequence #2: Second term is 3 and third term is 1 so first term is 9 (Ration term(n+1)/term(n) = 1/3)

 

L = 1/3 + 1 + 3

M = 9 + 3 + 1

 

M-L = 9 -1/3 = 26/3