Question

an electric refrigerator rated 400 watt is used for 8 hours a day an electric iron box rated 750 watt is used for 2 hours a day calculate the cost of using this appliances for 30 days if the cost of one kilowatt is rupees 3​

Answer 1

(1) - refrigerator

power = 400w

time. = 8 hrs

electrical energy = power* time

E. E. = 400/1000*8

= 3.2kwh

(2) - iron box

power = 750w

time. = 2hrs

electrical energy = 750/1000*2

= 1.5kwh

cost of 1kwh = rupees 3

cost of 1.5kwh = 4.5 rs

cost of month = 4.5*30

= 135 rs

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Answer 2

Given :

cost of one kilowatt = Rs 3

refrigerator rated 400 watt used for =  8 hours a day

and, an electric iron box rated 750 watt used for = 2 hours a day

To find :

The cost of using the appliances for 30 days .

Solution :

energy used in 1 day by refrigerator = 0.4 * 8 = 3.2 kwh

energy used in 1 day by iron box = 0.75 * 2 = 1.5 kwh

total energy used in a day = 3.2 + 1.5 = 4.7 kwh

energy used in 30 days = 4.7 * 30 = 141 kwh

cost of 141 kwh = 141 * 3 = Rs 423

The cost of using the appliances for 30 days is Rs 423 .