As we know that , the energy consumed = P * N * t
Given ,
tube lights P1 = 40 W, N1= 12, t1 = 4 hrs
television, P2 = 40 W, N 2= 3, t 2= 4 hrs
Bulb, P3 = 1000 W, N 3= 3, t 3= 2 hrs
So, electricity consumed by these three loads per day is given by ,
E1 = P1N1t + P2N2t2+ P3N3t3
= 40*12*4 + 40*3*4 + 100*2*2
=2800 Wh
= \(\frac{2800}{100}\)
= 2.8 unit
Thus in a month Electricity consumed is 2.8*30 = 84 unit (E1)
Similarly the electricity consumed by the electric iron in a week is E2 = 750*2*2 = 3000Wh
thus, in a month E2 = 3*4 = 12 unit
Total electricity consumed by the loads in a month at that house is 84+12 = 96 units
Hence, total cost to be paid = 96 * 7 = Rs. 672