# The effective resistance of a number of resistances connected in parallel is x ohm.When one of the resistances is removed,the effective resistance becomes y ohm.The resistance of the resister that is removed is?

$\fn_jvn \\\sum {1 \over R_i}={ 1 \over x} \\\sum {1 \over R_i}-{1 \over R_{removed}}={ 1 \over y} \\=>{1 \over R_{removed}}={ 1 \over x}-{ 1 \over y} \\=>R_{removed}={xy \over y-x}$