1) I have an electric blanket that was built for 110-220 volts. Can it be safely used in Australia?

2) Australia supplies electricity at 220-240 volts. Does that mean electricity can hit your appliances randomly at different voltages within that range?

Thank you

Here in the U.S. the terms 120 and 240 are "Nominal." The actual voltage may vary some but it will be within the range of 120/240 VAC +/- 10%.

1) The U.S. delivers 120 and 240 VAC at a frequency of 60 Hertz.

What is the freq. in Australia?

If for example it is 50 Hz. Then no the blanket will not work properly. You will need a matching transformer to supply the 60 Hz. To the blanket.

2) Appliances are normally made to work within a voltage range. For example, a printer's power supply may require a voltage of 150 VAC.