Final answer:
The given series is an arithmetic series and is infinite because it continuously increases by a constant value and lacks an endpoint.
Step-by-step explanation:
The given series, 1.05+1.10+1.15+1.20+..., is recognized as an arithmetic series due to the constant difference between consecutive terms, which in this case is 0.05. This increment of 0.05 characterizes the arithmetic progression of the series. Moreover, the series is classified as an infinite series because it lacks a specified endpoint, continuing indefinitely. The unending nature of this series implies that one can continually add terms, each elevated by 0.05 from its predecessor, making it an unbounded sequence of values. This infinite characteristic distinguishes it from finite arithmetic series with a defined number of terms.