Higher resistance of hair dryer

[thschica]

A hair dryer has two settings: 840 W and 1320 W.
(a) At which setting do you expect the resistance to be higher?
840 W correct
After making a guess, determine the resistance at each setting.
(b) 840 W setting

(c) 1320 W setting

Homework Equations

I am not exactly sure what equation to use to determine the resistance of the two settings.

The Attempt at a Solution

i tried numerous equations such as R =pla but i can't figure it out

 

[berkeman]

I don't understand the "guess" part of the question, but whatever.

Use the equation for power as a function of voltage and resistance. If you are in the US, then wall power for a hair dryer would typically be 110Vrms.