Question 15

A person sold a book for Rs 21 and got a loss percentage which was numerically equal to the cost price. What is the cost price (in Rs) of the book?

Solution

Selling price of book = Rs. 21

Let cost price = Rs. $$x$$

=> Loss % = $$x\%$$

According to ques,

=> $$\frac{(x-21)}{x}\times100=x$$

=> $$100x-2100=x^2$$

=> $$x^2-100x+2100=0$$

=> $$x^2-30x-70x+2100=0$$

=> $$x(x-30)-70(x-30)=0$$

=> $$(x-30)(x-70)=0$$

=> $$x=30,70$$

$$\therefore$$ Cost price (in Rs) of the book = Rs. 30 or 70

=> Ans - (C)


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