Question

find the energy in kWh consumed in 10hrs by 4 devices of power 500w each

Answer 1

power = 500 W =0.5 kW
time = 10 h
power = energy / time
0.5 = E/10
0.5 * 10 = E  
E = 5 kWh
now ,
energy consumed by 4 machines = 4 * 5 = 20 units

i hope it helps................. 

Answer 2

Power consumed by each device = 500W = 0.5 kW

Energy consumed by each one in 10 hours -

Power = Energy / Time
0.5 = Energy / 10
Energy = 10 × 0.5
Energy = 5 kWh

Therefore, power consumed by 4 such devices = 4 × 5 kWh
= 20 kWh
= 20 units