Question

The total cost price of certain number of books is $450$. By selling the books at $50$ each, a profit equal to the cost price of $2$ books is made. Find the approximate number of books.

• A. $13$
• B. $11$
• C. $15$
• D. $25$

Answer 1

The correct option is B $11$

Let the book bought be $x$.
Selling price of x book is $\frac{450\times 2}{x}$
The book seller sells all the book for the total of $50x$, which is more than the $450$ cost of all the books.
The difference is the profit, so
$50x-450=\frac{900}{x}$
$50x^2-450x-900=0$
On factoring, we get
$(x-10.6)(x+1.6)=0$
$x=10.6$ or $-1.6$
Therefore, the number of books bought is approximately $11$.