Without evaluating their sums

MATHEMATICS · Subjective · A Level · Mathematics · Sequences and series · Sequences and series

Problem

Without evaluating their sums, decide which of the following two infinite geometric series has the greater sum and give one brief reason. Series P:

2 + 1.2 + 0.72 + \ldots

Series Q:

2 + 0.8 + 0.32 + \ldots