Given that, 3 men paint a house in 20 days.
Now, we have to find the number of days, when 30 men take to do the same work.
Let x be the no. of days by 30 men.
As we know the number of men and number of days is indirectly proportional to each other. Because, if the number of men increases, the days will decrease.
20/x = 30/3
20/x = 10
x = 20/10
x = 2
Hence, 2 days is required to do the same work by 30 men.