The cost price of a chair is 21.800. Later, its cost price becomes 22,100. What is the percentage increase in the cost price of the chair?

Percentage increase is obtained from the standard relation

$$\text{Percentage increase}=\frac{\text{New price}-\text{Original price}}{\text{Original price}}\times100\%$$

Original (old) cost price of the chair $$=Rs.\,1\,800$$
New cost price of the chair $$=Rs.\,2\,100$$

Increase in cost price
$$\text{Increase}=2\,100-1\,800=300$$

Substituting in the formula,

$$\text{Percentage increase}=\frac{300}{1\,800}\times100\%$$

Simplifying the fraction,

$$\frac{300}{1\,800}=\frac{1}{6}$$

Hence,

$$\text{Percentage increase}=\frac{1}{6}\times100\%=16\frac{2}{3}\%$$

Therefore, the cost price of the chair has increased by $$16\frac{2}{3}\%$$.

Option B which is: $$16\frac{2}{3}\%$$