Two electric dipoles of moment P and 64 P are placed in opposite direction on a line at a distance of 25 cm. The electric field will be zero at point between the dipoles whose distance from the dipole of moment P is 

Suppose neutral point N lies at a distance x from dipole of moment p or at a distance x₂ from dipole of 64 p.

$\text{ At }\mathrm{N}\mid \text{ E. F. due to dipole (1) }|=|\text{ E. F. due to dipole (2) }\mid$

$\begin{array}{l}\Rightarrow \frac{1}{4{\mathrm{\pi \epsilon }}_0}\cdot \frac{2\mathrm{p}}{{\mathrm{x}}^3}=\frac{1}{4{\mathrm{\pi \epsilon }}_0}\cdot \frac{2\left(64\mathrm{p}\right)}{(25-\mathrm{x}{)}^3}\\ \Rightarrow \frac{1}{{\mathrm{x}}^3}=\frac{64}{(25-\mathrm{x}{)}^3}\Rightarrow \mathrm{x}=5\mathrm{cm}.\end{array}$