10 people can dig a trench in 6 days. How many people can dig it in 4 days?
Let x people dig the trench in 4 days.
More people will take less number of days to dig the trench. Hence, this is a case of inverse proportion.
Now,$10 \times 6=x \times 4$
∴ 15 people can dig the trench in 4 days.