Profit and Loss [लाभ और हानि]–07

Question: If I purchased 11 books for Rs.10 and sold 10 books for Rs.11, then what is  the profit percent ? [यदि 11 किताबों को 10 रूपये में ख़रीदा जाता है और 10 किताबों को 11 रूपये में बेच दिया जाता है, तो बताएं कि कितना प्रतिशत लाभ हुआ?]  [Ans. (b) 21%]

(a) 10%     (b) 21%     (c) 11%    (d) 100%    (e) None of these

Solution:

Detailed Solution: Profit or loss can be calculated, if and only if the number of articles sold and bought, are the same. And, the same is true for the profit or loss percent also.

In this question, no. of books sold and bought are not the same. For profit or loss percent, we must make them same. In general, we calculate the cost price and selling price of one article. But in this case, calculation becomes tough.

For example, cost price of one article is Rs 11/10 and the selling price of one article is 10/11. These numbers are not easy to calculate, so we avoid them. And proceed in a way, so that we can feel easy and relaxed.

We take LCM of 11 and 10 (no. of articles bought and sold), which is 110. Now we will bought 110 articles and sold again 110 articles.

Given that CP (cost price) of 11 articles is Rs 10, so CP of 110 articles becomes Rs. 100

Also, SP (selling price) of 10 articles is Rs 11, so SP of 110 articles becomes Rs. 121

Therefore, the profit is Rs. 21 (121-100), which is out 100 (since cost price is Rs. 100), profit percent is 21% Ans.