Sure. The formula for an infinite geometric series with first term a and common ratio r says it converges when |r|<1; in that case the sum is
[tex]S = \dfrac{a}{1-r}[/tex]
Q3. r=-4/5 (converges), a=5, S=5/(1- -4/5) = 5/(9/5) = 25/9
Answer: a
Q4. r=1/6 (converges), a=420, S=420/(1-1/6) = 420/(5/6) = 6(84) = 504
Answer: a
Q5. r=1.2, diverges
