Question

A dealer sells a particular product for Rs. $39$ and gains as much percent as the cost price of the product. Find the cost price of the particular product.

• A. Rs. $10$
• B. Rs. $20$
• C. Rs. $30$
• D. Rs. $40$

Answer 1

Answer: (C)

Rs. $30$

Let the C.P. of the product be $x$
Gain $\%=x\%$
Gain $=x\%$ of $x=$ $\frac{x^2}{100}$
S.P. $=$ C.P. $+$ gain
S.P. $=39$
Therefore, $x+\frac{x^2}{100}=39$

$100x+x^2=3900$
$x^2+100x-3900=0$

$x^2+130x-30x-3900=0$

$x(x+130)-30(x+130)=0$

$(x+130)(x-30)=0$
$x=-130$ or $30$
Price cannot be negative,
So, cost price of the particular product $=$ Rs. $30$