A shopkeeper bought 20 chairs for ₹18,000. On selling them he had a gain equal to the selling price of four chairs. What is the selling price of each chair ?

Cost price (CP) of 20 chairs = ₹18,000.

Gain is equal to the selling price (SP) of 4 chairs. 

simple ratio and proportion;

x : y :: a : b 

​$$\implies \frac{x}{y} = \frac{a}{b}$$ 

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