Discussion

If the selling price of 10 articles is equal to the cost price of 11 articles, find the gain per cent.

Answer: C

The gain is 10%.

Let the cost price of one article be Rs. 1. Then the selling price of 10 articles equals the cost of 11 articles, Rs. 11.

\[ \begin{aligned} \text{gain} &= 11 - 10 = 1 \\ \text{gain\%} &= \frac{1}{10} \times 100 = 10\% \end{aligned} \]

The gain is reckoned on the cost price of the 10 articles sold, Rs. 10. Dividing by 11 instead gives about 9.1%, which is not offered.

A shortcut for such questions: when the selling price of x articles equals the cost price of y articles, the gain per cent is (y − x)/x × 100.

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