Question:
Three spraying machines working together can finish painting a house in 60 minutes. How long will it take for 5 machines of the same capacity to do the same job?
Solution:
Let the time taken by 5 spraying machines to finish a painting job be x minutes.
Since the number of spraying machines and the time taken by them to finish a painting job are in inverse variation, we have:
$3 \times 60=5 \times x$
$\Rightarrow 180=5 x$
$\Rightarrow x=\frac{180}{5}$
$=36$
Thus, the required time will be 36 minutes.