Question

A person sold his watch for Rs. $144$. If the percentage of his profit was equal to the cost price then the watch would have cost him

• A. Rs. $100$
• B. Rs. $90$
• C. Rs. $85$
• D. Rs. $80$

Answer 1

The correct option is D Rs. $80$

Let C.P.$=$ Rs. $x$, S.P. $=$ Rs. $144$, Profit $=x\%$ $\therefore x+x\%$ of $x=144$
$\Rightarrow x+\frac{x}{100}\times x=144$
$\Rightarrow x^2+100x-14400=0\Rightarrow x^2+180x-80x-14400=0$
$\Rightarrow x(x+180)-80(x+180)=0$
$\Rightarrow (x+180)(x-80)=0\Rightarrow x=-180or80$
Neglecting negative value $x=80$.