Question

Three spraying machines working together can finish painting a house in 60 minutes. How long will it take 5 machines of the same capacity to do the sane job ?

Answer 1

Let in x minutes, 5 machines can do the work
Now
$\begin{array}{ccc}\text{Machines}& 3& 5\\ \text{Period (minutes)}& 60& x\end{array}$
More machines, less period
$\therefore$ By inverse variation . $3:5=x:60\Rightarrow \frac{3}{5}=\frac{x}{60}$
$\Rightarrow 5\times x=3\times 60\Rightarrow x=\frac{3\times 60}{5}=36$
$\Rightarrow$ 5 machines can do the work in = 36 minutes