A parallel combination of three resistors takes a current of 7.5 A form a 30 V supply, It the two resistors are $ 10 \Omega $ and $ 12 \Omega $. find which is the third one?
$ I = 7.5 A , V = 30 V, R_1 = 10 \Omega , R_2 = 12 \Omega , R_3 = ? $ $ R_{net} = { V \over I}$ $ \Rightarrow { 1 \over Rnet }= {I \over V} = { 1 \over R_1 } + { 1 \over R_2 } + { 1 \over R_3 } $
