A 2 kW electric fire is switched on for 30 minutes. How many Units of electricity does it use?

Units of electricity are measured in kWh (kilowatt-hours).
We have our power in kW (2 kW)
We have our time in minutes (30 minutes)
Looking at the units, we can see that:
kW x minutes = kWminutes (kWm)
and
kW x hours = kWhours    (kWh)
 
So, to get our answer in kWh, we must first convert our time to hours:
30 minutes = 0.5 hours
 
then
2 kW x 0.5 hours = 1 kWh
 
So our answer is 1 kWh.