A dealer gets Rs 30 less if instead of selling a chair at a gain of 12% he sells it at a gain of 8%.

Let the $\mathrm{CP}$ be $\mathrm{Rs} x$.

Then, we have:

$(12 \%$ of $\mathrm{x})-(8 \%$ of $\mathrm{x})=30$

$\Rightarrow\left(\mathrm{x} \times \frac{12}{100}\right)-\left(\mathrm{x} \times \frac{8}{100}\right)=30$

$\Rightarrow\left(\frac{12 \mathrm{x}}{100}-\frac{8 x}{100}\right)=30$

$\Rightarrow \frac{4 x}{100}=30$

$\Rightarrow x=\left(30 \times \frac{100}{4}\right)$

= 750

$\therefore$ The cost price of the chair is Rs 750 .