Question

A dealer sells a jewel for Rs. $11$ and gains as much percent as the cost price of the jewel. Find the cost price of the jewel.

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

Answer 1

The correct option is A Rs. $10$

Let the C.P. of the jewel be $x$
Gain $\%=x\%$
Gain $=x\%$ of $x=\frac{x^2}{100}$
S.P. $=$ C.P. $+$ gain
S.P. $=11$
Therefore, $x+\frac{x^2}{100}=11$
$100x+x^2=1100$
$x^2+100x-1100=0$

$x^2+110x-10x-1100=0$

$x(x+110)-10(x+110)=0$

$(x+110)(x-10)=0$
$x=-110$ or $10$
Price cannot be negative,
So, cost price of the jewel $=$ Rs. $10$