In a meter bridge a $30\;\Omega$ resistance is connected in the left gap and a pair of resistances P and Q in the right gap. Measured from the left, the balance point is 37.5 cm , when P and Q are in series and $71.4\;cm$ when they the parallel. The values of P and Q (in $\Omega$) are :

Question

\[\begin {array} {1 1} (a)\;40 \; 10 & \quad (b)\;35\;15 \\ (c)\;30\;20 & \quad (d)\;25\;25 \end {array}\]