This is a proportion question. You compare two ratios. Unfortunately it is an inverse ratio.
12 = k/100 Multiply both sides by 100
1200 = k
20 = k/x Multiply both sides by x
20x = k
20x = 1200 Divide by 20
20x/20 = 1200/20
x = 60 days.
An inverse proportion works by making a constant k. The constant k makes the days shorter when the number of people increases. You should expect that. More people , less time.
