Question

Some 200 W bulbs are used for 5 hours every day. if the cost of electricity at the rate of Rs 5 per kilowatt hour is Rs 750 for the month of June, then find the no of bulbs used

Answer 1

Hello Mate!

Month of june = 30 days.

So, for using x number of bulbs for a month or 30 days it cost Rs 750.

Then for 1 day it will cost = Rs 750/30 = Rs 25

Then for 1 hr it will cost = Rs 25/24 = Rs 1 ( approx ).

Now, each bulb consume 200 W in 5 hrs

In 1 hr it will consume = 200/5 or 40 W

Since 1 W = 1/1000 kW

40 W = 40/1000 kW or 0.04 kW

Now, x number of bulbs will consume 0.04 kW energy per hour which cost Rs 1 at the rate of Rs 5 per kW.

Cost of consuming energy = 0.04x × Rs 5

Cost of consuming energy = Rs 1

1 = 0.04x × 5

1 = 0.2x

1/0.2 = x

5 bulbs = x

Hence 5 bulbs are used.

Have great future ahead!