Question

$25$ picture postcards cost $Rs31.25$. How many postcards can be bought in $Rs23.75$?

Answer 1

Given. postcards cost of $25$ pictures$=Rs31.25$

postcards cost of $k$ pictures $=Rs23.75$

As the cost increases,the number of pictures also increases in the same ratio. It is a case of direct proportion.

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

Suppose the cost is $\text{'}x\text{'}$ the number of pictures is $\text{'}y\text{'}.$.

$$\begin{gathered} x_1=31.25;x_2=23.75 \\ {y}_1=25;y_2=k \end{gathered}$$

$$\begin{gathered} \frac{31.25}{23.75}=\frac{25}{k} \\ 31.25\times k=25\times 23.75 \\ k=\frac{{\displaystyle \stackrel{19}{\cancel{23.75}}}\times {\displaystyle \cancel{25}}}{{\displaystyle \underset{\cancel{1.25}}{\cancel{31.25}}}} \\ k=19 \end{gathered}$$

Hence the Picture postcards in $Rs23.75$ is $19$