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Question
In a house two 60 W electric bulbs are lighted for 4 hours, and three 100 W bulbs for 5 hours everyday. Calculate the electric consumed in 30 days.
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Solution
Power of bulb 1, P1 = 60 W
Duration that it was lit, t1= 4 h
Electric energy consumed by two bulbs, E1 = 2 x P1 x t1
= 2 x 60 x 4
= 480 Wh
Power of bulb 2, P2 = 100 W
Duration that it was lit, t2= 5 h
Electric energy consumed by three bulbs, E2= 3 x P2x t2 = 3 x 100 x 5 = 1500 Wh
Total electric energy consumed in 30 days, E = 30 x (E1+ E2)
E = 30 x (480 + 1500)
E = 30 x 1980
E = 59400 Wh
E = 59.4 kWh
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