In Janpath, the cost of a packet of coffee is Rs. 240. One shopkeeper advertises coffee at $\dfrac{1}{5}$ off, and another shopkeeper offers $\dfrac{1}{10}$ off. Which is a better buy? Why? What is the difference in the price at which it is sold?
ANSWER
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Hint: Find the price at which the coffee is sold by each of the shopkeepers and compare the prices. The one selling at a lower price is better to buy. Hence find the difference in the selling prices of the coffee by each shopkeeper.
Complete step-by-step answer: Cost of one coffee = Rs. 240 Since the first shopkeeper offers $\dfrac{1}{5}$ times off on the total price, the selling price of the coffee by the first shopkeeper $=240-\dfrac{240}{5}=240-48=192$ Hence the first shopkeeper sells the coffee at Rs 192 per packet. Since the second shopkeeper offers $\dfrac{1}{10}$ times off on the total price, the selling price of the coffee by the second shopkeeper $=240-\dfrac{240}{10}=240-24=216$ Hence the second shopkeeper sells the coffee at Rs 216 per packet. Hence we should buy coffee from the first shopkeeper. Also, the difference in selling prices = 216-192 =Rs. 24
Note: We can also calculate the selling price by knowing what fraction of the original cost price is the coffee being sold. Since the first shopkeeper offers $\dfrac{1}{5}$ off, he sells the coffee at $\dfrac{4}{5}$ of the original price $=\dfrac{4}{5}\times 240=192$ Hence the first shopkeeper sells the coffee at Rs 192 per packet. Similarly, the second shopkeeper sells the coffee at $\dfrac{9}{10}$ of the original price $=\dfrac{9}{10}\times 240=216$ Hence the second shopkeeper sells the coffee at Rs 216 per packet.