The percentage of profit, when an article is sold for Rs.78 is twice that when it is sold for Rs.69. The cost price of the article is : किसी वस्तु को 69 रू. में बेचने के बजाय 78 रू. में बेचने पर लाभ की प्रतिशतता दुगुनी है । उस वस्तु का क्रय मूल्य है-

Let cost price be C. When sold for Rs.69, profit percent equals (69 minus C) over C times 100. When sold for Rs.78, profit percent equals (78 minus C) over C times 100. Given that (78 minus C) over C equals 2 times (69 minus C) over C. Solving gives 78 minus C equals 2 times (69 minus C), so 78 minus C equals 138 minus 2C, giving C equals 60.