The resistance of the series combination of two resistance is S. When they are joined in parallel the total resistance is P. If S = nP, then the minimum possible value of n is

If two resistances are R1 and R2, thenS=R1+R2   and  P=R1R2R1+R2From given condition, S = nPor  R1 +  R2=nR1R2R1+R2⇒  R1+R22 =  nR1R2  ⇒    R1−R22  +  4R1R2=nR1R2So  n=4+R1−R22R1R2.  Hence, minimum value of n is 4.