If 15 people can build a house in 48 days, what are the number of workers required to complete it in 30 days?

If the number of workers building the house increases, the number of days required to build the house decreases.
∴This is a case of inverse proportion.

So, by inverse proportion,

 $x_1{y}_1=x_2{y}_2$

$15\times 48=x_2\times 30$

$x_2=\frac{720}{30}$

$x_2=24$