If the cost price of 18 chairs be equal to selling price of 16 chairs,

Let the cost price of one chair be Rs. C, and selling price be Rs. S

There fore, $18 \mathrm{C}=16 \mathrm{~S}$

$\mathrm{C}=\frac{16}{18} \mathrm{~S}$

As cost price is less than the selling price,

S. P. $=\left(\frac{100+\text { profit } \%}{100}\right)$ C.P

$\mathrm{S}=\left(\frac{100+\text { profit } \%}{100}\right) \mathrm{C}$

$\frac{\mathrm{S}}{\mathrm{C}}=\left(\frac{100+\text { profit } \%}{100}\right)$

$\frac{18}{16}=\left(\frac{100+\text { profit } \%}{100}\right)$

$\frac{1800}{16}=100+$ profit $\%$

$\frac{1800}{16}-100=$ profit $\%$

$P$ rofit $\%=\frac{1800-1600}{16}$

$=\frac{200}{16}$

$=12.5$

Therefore, the required profit percent is $12.5 \%$.