Question

The average rainfall in a town is $19.6cm$ in $4$ weeks. How much rain falls on an average , in $17$ days $?$

Answer 1

Given, $19.6cm$ rainfall in $4$ weeks $[\because 1week=7days]$

$19.6cm$ rainfall $=4\times 7=28days$

Let, the average rainfall in $17$ days $=kcm$

As the number of days increases, the average rainfall 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 number of days is $\text{'}x\text{'}$ the average rainfall is $\text{'}y\text{'}.$.

$$\begin{gathered} x_1=28;x_2=17 \\ {y}_1=19.6;y_2=k \end{gathered}$$

$$\begin{gathered} \frac{28}{17}=\frac{19.6}{k} \\ 28\times k=17\times 19.6 \\ k=\frac{{\displaystyle \stackrel{0.7}{\cancel{19.6}}}\times {\displaystyle 17}}{{\displaystyle \underset{1}{\cancel{28}}}} \\ k=11.9cm \end{gathered}$$

Hence, the average rainfall in $17$ days is $11.9cm$.