Find the energy in kWh consumed in 10 hours by four devices of power 500 W each.

Power of each device, P = 500 W = 0.5 kW
Time for which the devices are used, t = 10 hours
Thus energy consumed by 4 devices, E = 4 × P × t
E = 4 × 0.500 × 10 kWh
E = 20 kWh