Question

The cost of printing a book of $220$ pages in $Rs660$. What would be the cost of printing a book with $180$ pages ?

Answer 1

Let cost of printing books $=x$

Number of pages $=y$

The cost of printing a book of $220$ pages $=Rs660$

The cost of printing a book of $180$ pages $=x$

As the number of pages decreases, cost of painting books also decreases in the same ratio. It is a case of direct proportion.

We make use of the relation of type $\frac{x_1}{x_2}=\frac{y_1}{y_2}$

$x_1=660;x_2=x;y_1=220;y_2=180$

So,

$\frac{660}{x}=\frac{220}{180}$

$$\begin{gathered} 220\times x=660\times 180 \\ x=\frac{660\times 180}{220} \\ x=\frac{{\displaystyle \stackrel{3}{6\cancel{60}}}\times 180}{\cancel{220}} \\ x=3\times 180 \\ \therefore x=540 \end{gathered}$$

Hence the cost of printing a book of $180$ pages is $Rs.540$