Power of biconvex lens is P diopter. When it is cut into two...

Power of equiconvex lens $=P$ i.e $P=\frac{1}{f}$, where $f$ is focal length of equiconvex lens. When an equiconvex lens is cut into two symmetrical halves by a plane containing the principal axis, then its focal length remains same. Hence, power of lens (each halves) $$\begin{aligned} & P^{\prime}=\frac{1}{f} \Rightarrow P^{\prime}=P \\ & \Rightarrow \quad \frac{P^{\prime}}{P}=1 \\ & \Rightarrow \quad P: P=1: 1 \end{aligned}$$