What is the potential difference across the lamp? How much resistance was added to the circuit? How much power is now dissipated in the lamp?

Question

A 20 W lamp is connected to 120 V, and its current is measured. A resistor is added to the lamp to reduce the current to half its original value.

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Answer 1 · 2016-02-16T16:34:53

I found:
#R_1=727Omega#
#P_1=4.95W#
#V_("lamp")=59.6V#

Have a look (but check my maths):

enter image source here
The potential difference across the lamp will be:
#V_("lamp")=R_("lamp")I_1=718.5*0.083=59.6V#