How many significant figures should there be in the answers to the following multiplications and divisions?

a) [[$ 12 \cdot \text{0.5} $]]


b) [[$ \text{0.1} \cdot \text{2.5} $]]


c) [[$ \text{3.21} : 45 $]]


d) [[$ \text{0.245} : \text{0.12} $]]