Question

Four bulbs, each of rating (100 W, 220 V) and
connected in parallel across a voltage supply of
220 V, are operated for five hours daily. If all the bulbs
are replaced by LEDs of rating (8 W, 220 V), how
many units of electrical energy will be saved every
month (30 days)?
(1) 55.2 units
(2) 60 units
(3) 4.8 units
(4) 32 units

Answer 1

power=100 w
total hours in 30 days = 5*30=150 hrs 
energy= power*time
power= 0.1 kw
0.1*150=15 
power for four bulbs = 4*15= 60 kw
now 
for led apply same method 
  power = 8 w
total hours in 30 days = 150 
power = 0.008 k/w
energy = power *time 
=0.008*150
=1.2
so  power for four bulbs = 1.2*4=4.8
sow we have to find the energy save so p1-p2 = 60-4.8=55.2 ans 

so option a is correct 

Answer 2

Answer:

Explanation:

power=100 w

total hours in 30 days = 5*30=150 hrs 

energy= power*time

power= 0.1 kw

0.1*150=15 

power for four bulbs = 4*15= 60 kw

now 

for led apply same method 

  power = 8 w

total hours in 30 days = 150 

power = 0.008 k/w

energy = power *time 

=0.008*150

=1.2

so  power for four bulbs = 1.2*4=4.8

sow we have to find the energy save so p1-p2 = 60-4.8=55.2