Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

From Joule's Law of heating, P = V²/R
For first lamp, R₁ = 220²/100
For second lamp, R₂ = 220²/60
When they are connected in parallel,
1/Req = 1/R₁ + 1/R₂ = 1/(220²/100) + 1/(220²/60)
⇒ Req = 220²/160
From Ohm's Law, V = I Req
220 = I (220²/160)
I = 0.73 A