Question

in an household an electric bulb of 100 W is used for 10 hours and an electric heater of 1000W is used for 2 hours . calculate 1- ) the cost of using bulbs and the heater for 30 days .take the cost of one unit of electrical energy as 5 rupees.?

Answer 1

Hi there! I have the complete solution:
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Given that,100 W =  bulb is used for 10 hours. 
This means for one hour = 100/10 = 10 W per hour       .....(i)

Now, heater of  1000 W is used for 2 hours.
This means for one hour = 1000/2 = 500 W per hour         ....(ii)

Together they cost: (i) + (ii) = 10 + 500 = 510 W per hour

In 30 days, we have 510 x 30 = 15300 W.

Now, 1000 W = 1 KW

So, 15300 W = 15.3 KWH or 15.3 units

Now, 1 unit = 5 Rs.

Hence, the cost for 15.3 units = 5 x 15.3 =
 
Ans. Rs. 76.5
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I hope this helps.

Answer 2

Energy used by heater =100wx(10hx30days) =30000wh =30unit

Energy used by bulbs =1000w(2h ×30days) =60kwh =60units

Total Energy = 60+30 =90Units

Cost =90×5 =450 rupees