Question:
In a hostel of 50 girls, there are food provisions for 40 days. If 30 more girls join the hostel, how long will these provisions last?
Solution:
Let $x$ be the number of days with food provisions for 80 (i.e., $50+30$ ) girls.
Since the number of girls and the number of days with food provisions are in inverse variation, we have:
$50 \times 40=80 x$
$\Rightarrow x=\frac{50 \times 40}{80}$
$=\frac{2000}{80}$
$=25$
Thus, the required number of days is 25 .