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Two bulbs of 40W each are lighted for eight hours daily. Find the cost of electrical energy consumed by them in one week at Rs. 3 per unit.

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Best answer

Given 

Power = 40W 

Time = 8 hours 

Now

Power = \(\frac{Energy}{Time}\)

⇒ 40 = \(\frac{Energy}{8}\)

⇒Energy = 40 x 8 = 320

Energy consumed by 2 bulbs in 1 week = 320×2×7 = 4480 Wh = 4.48 kW 

(∵ 1kWh = 1000Wh) 

Total units = 4.48 units

Now 

Cost of 1 unit = Rs 3 

Total cost = 4.48 ×3 = Rs13.44 

Total cost for 1 week is Rs 13.44

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