If a store sells a commodity at a 10% discount on the price (i.e. 10% discount), it can still make a profit of 20%. If the price of the commodity is 28 yuan per unit, the purchase price of the commodity is () A. 21 yuan B. 19.8 yuan C. 22.4 yuan D. 25.2 yuan
Let the purchase price of the commodity be x yuan. From the meaning of the question, we get: (1 + 20%) x = 28 × (1-10%), and the solution is: x = 21, so we choose a